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This manuscript examines the relationship between child mortality and subsequent fertility using longitudinal data on births and childhood deaths occurring among 15,291 Tanzanian mothers between 2000 and 2015. Generalized hazard regression analyses assess the effect of child loss on the hazard of conception, adjusting for child-level, mother-level, and contextual covariates. Results show that time to conception is most reduced if an index child dies during the subsequent birth interval, representing the combined effect of biological and volitional replacement. Deaths occurring during prior birth intervals were associated with accelerated time to conception during future intervals, consistent with hypothesized insurance effects of anticipating future child loss, but this effect is smaller than replacement effects. The analysis reveals that residence in areas of relatively high child mortality is associated with hastened parity progression, again consistent with the insurance hypothesis. Investigation of high-order interactions suggests that insurance effects tend to be greater in low-mortality communities, replacement effects tend to be stronger in high-mortality community contexts, and wealthier families tend to exhibit a weaker insurance response but a stronger replacement response to childhood mortality relative to poorer families., (Copyright © 2023 The Authors.)

Background: In developing countries, short birth interval is one of the major public health issues. It is one of the leading cause's adverse birth outcomes in the worldwide. Despite the fact that ending maternal and perinatal morbidity and mortality is one of the Sustainable Development Goals (SDG), the burden of the problem continues to be a huge concern in developing countries, including high fertility countries. Thus, this study aimed to determine the short birth interval and its predictors in ten high fertile sub-Saharan African countries., Methods: Data for this study was obtained from the most recent Demographic and Health Surveys (DHS). A total of weighted sample of 303,979 women of childbearing age group (15- 49) who had at least two alive consecutive children was included. A multilevel mixed-effect binary logistic regression model was fitted to identify the associated factors of short birth interval. As a final step, the Adjusted Odds Ratio (AOR) was used with a confidence interval of 95% in determining statistical significance., Results: Overall prevalence of short birth interval in high fertile sub Saharan Africa was 58.74% (52.32%, 65.17%).The factors significantly associated with the short birth interval were women's educational status; primary education (AOR = 0.88; 95% CI: 0.86,0 .91), secondary and higher (AOR = 0.10; 95% CI: 0.09, 0.11), working (AOR = 0.91; 95% CI: 0.88, 0 .93), classified as rich wealth index level (AOR = 0.90; 95% CI: 0.88, 0.93),having six and above ideal number of children (AOR = 2.25; 95% CI: 2.22, 2.30), preferred waiting time two years and above to give birth (AOR = 0.83; 95% CI: 0.76, 0.89), contraceptive non users (AOR = 3.01; 95% CI: 2.93, 3.07), community level education (AOR = 1.97; 95% CI: 1.54, 2.08), rural residency (AOR = 2.17; 95% CI: 2.13, 2.22), and country Chad (AOR = 1.37; 95% CI: 1.22, 1.54)., Conclusion: The prevalence of short birth interval in the top ten high fertile sub Saharan African countries is still optimally high. Therefore, the government of each country should work on the access to family planning and education in rural parts of the countries., (© 2023. The Author(s).)

Since the advent of prenatal sex-determination technologies in the mid-1980s, India has experienced an increasingly male-biased sex ratio at birth, presumably from sex-selective abortions. Abortions lengthen birth intervals, but we know little about how birth spacing has changed or the effects of these changes. I show that, although the overall length of birth intervals increased from 1970 to the mid-2010s, well-educated women with no sons had the most substantial lengthening, as well as the most male-biased sex ratios. Furthermore, most of these changes took place immediately after the introduction of prenatal sex-determination technologies. Consequently, some women without sons now have longer birth intervals than those with sons, reversing India's traditional spacing pattern. Women with low education continue short birth spacing when they have no sons, with only limited evidence of male-biased sex ratios. Because of the rapid lengthening of birth intervals, period fertility rates substantially overestimated how fast cohort fertility fell. Moreover, predicted cohort fertility is still 10%-20% above the period fertility rate. If the lengthening of birth intervals arises from repeated abortions, the associated short pregnancy spacing may counteract any positive effects of longer birth spacing. There is, however, no evidence of this effect on infant mortality. Judging from sex ratios, sex-selective abortion use is not declining., (Copyright © 2021 The Author.)

We analysed population data from the 2015-16 National Family Health Survey to disentangle the intricate underlying effects of reproductive behaviours and fertility preferences on child growth. We expected birth interval length to be more strongly associated with stunting than sibsize and these effects to be moderated by whether the child was wanted or unintended (mistimed/unwanted). Regression analyses showed strong and equal effects of short birth interval and sibsize on stunting, when adjusted for potential confounders and unobserved between-mother heterogeneity. There were no statistical associations between stunting and mistiming/unwantedness of index children, suggesting the absence of discrimination against such children. We conclude that while fertility preferences have no effect, reproductive behaviours exert significant influence on child growth. Sibsize has been falling for many years in India but birth interval lengths have remained largely unchanged. The results underscore the need for strengthening uptake of reversible contraceptives to enable longer birth intervals.

In this cross-sectional study, we evaluated data from the 2014 Bangladesh Demographic and Health Survey (BDHS), which consisted of 7,707 married women aged 15-49 years who lived with at least one child younger than 5 years. This study's primary aim was to examine the relationship between maternal high-risk fertility behavior and child morbidity. To define high-risk fertility behaviors, we considered three variables: maternal age at the time of delivery, birth order, and birth interval. The main outcome measures were mortality-related disease in the past 2 weeks (acute respiratory infection [ARI], diarrhea, and fever) and low birth weight (LBW). We used modified Poisson regression with generalized estimating equations to assess the relationships between the variables of interest. Results indicate that a substantial portion of women (34%) exhibited high-risk fertility patterns; 28.7% engaged in a single high-risk behavior and 5.4% engaged in multiple high-risk behaviors. After adjusting for relevant covariates, high-risk fertility behaviors were significantly associated with an increased likelihood of ARI (adjusted relative risk [ARR]: 1.22, 95% CI: 1.05-1.50), diarrhea (ARR: 1.18, 95% CI: 1.03-1.35), fever (ARR: 1.29, 95% CI: 1.11-1.58), and LBW (ARR: 1.27, 95% CI: 1.10-1.52). In addition, engaging in multiple high-risk fertility behaviors appeared to have far-reaching consequences on the outcomes measured. Maternal high-risk fertility behaviors are important predictors of morbidity in children younger than 5 years. Preventing high-risk fertility behavior may reduce childhood morbidity and mortality in Bangladesh.

Objectives: We described the trend of fertility rates, age-specific fertility rates and associated factors in Finland over a 30-year period., Design: A descriptive population-based register study., Setting: Fertility data, including age at first birth, childlessness and educational levels were gathered from the Finnish Medical Birth Register and Statistics Finland., Participants: All 1 792 792 live births from 1987 to 2016 in Finland., Main Outcome Measures: Completed fertility rate, total fertility rate and age-specific fertility rate., Results: The total fertility rate of Finnish women fluctuated substantially from 1987 to 2016. Since 2010, the total fertility rate has gradually declined and reached the lowest during the study period in 2016: 1.57 children per woman. The mean maternal age at first birth rose by 2.5 years from 26.5 years in 1987 to 29 years in 2016. The proportion of childless women at the age of 50 years increased from 13.6% in 1989 to 19.6% in 2016. By considering the impact of postponement and childlessness, the effect on total fertility rates was between -0.01 and -0.12 points. Since 1987, the distribution of birth has declined for women under the age of 29 and increased for women aged 30 or more. However, start of childbearing after the age of 30 years was related to the completed fertility rate of less than two children per woman. The difference in completed fertility rate across educational groups was small., Conclusions: Postponement of first births was followed by decline in completed fertility rate. Increasing rate of childlessness, besides the mean age at first birth, was an important determinant for declined fertility rates, but the relation between women's educational levels and the completed fertility rate was relatively weak., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: To investigate the association of socioeconomic position (SEP) with reproductive outcomes among Australian women., Methods: Data from the Australian Longitudinal Study on Women's Health's (population-based cohort study) 1973-1978 cohort were used (N = 6899, aged 37-42 years in 2015). The association of SEP (childhood and own, multiple indicators) with age at first birth, birth-to-pregnancy (BTP) intervals and total number of children was analysed using multinomial logistic regression., Results: 14% of women had their first birth aged < 24 years. 29% of multiparous women had a BTP interval within the WHO recommendation (18-27 months). Women with a low SEP had increased odds of a first birth < 24 years: low (OR 7.0: 95% C.I. 5.3, 9.3) or intermediate education (OR 3.8: 2.8, 5.1); living in rural (OR 1.8: 1.5, 2.2) or remote (OR 2.1: 1.7, 2.7) areas; who found it sometimes (OR 1.8: 1.5, 2.2) or always difficult (OR 2.0: 1.6, 2.7) to manage on their income; and did not know their parent's education (OR 4.5: 3.2, 6.4). Low SEP was associated with having a much longer than recommended BTP interval., Conclusion: As the first Australian study describing social differences in reproductive characteristics, these findings provide a base for reducing social inequalities in reproduction. Assisting adequate BTP spacing is important, particularly for women with existing elevated risks due to social disadvantage; including having a first birth < 24 years of age and a longer than recommended BTP interval. This includes reviewing services/access to postnatal support, free family planning/contraception clinics, and improved family policies.

Although research on the fertility response to childhood mortality is widespread in demographic literature, very few studies focused on the two-way causal relationships between infant mortality and fertility. Understanding the nature of such relationships is important in order to design effective policies to reduce child mortality and improve family planning. In this study, we use dynamic panel data techniques to analyse the causal effects of infant mortality on birth intervals and fertility, as well as the causal effects of birth intervals on mortality in rural Bangladesh, accounting for unobserved heterogeneity and reverse causality. Simulations based upon the estimated model show whether (and to what extent) mortality and fertility can be reduced by breaking the causal links between short birth intervals and infant mortality. We find a replacement effect of infant mortality on total fertility of about 0.54 children for each infant death in the comparison area with standard health services. Eliminating the replacement effect would lengthen birth intervals and reduce the total number of births, resulting in a fall in mortality by 2.45 children per 1000 live births. These effects are much smaller in the treatment area with extensive health services and information on family planning, where infant mortality is smaller, birth intervals are longer, and total fertility is lower. In both areas, we find evidence of boy preference in family planning.

We describe a regression-based approach to the modelling of age-, order-, and duration-specific period fertility, using retrospective survey data. The approach produces results that are free of selection biases and can be used to study differential fertility. It is applied to Demographic and Health Survey data for Ethiopia, Kenya, Tanzania, and Zimbabwe to investigate differential trends in fertility by education. Parity progression fell and the intervals following each birth lengthened between the 1970s and 2000s in all four countries. Fertility fell most among women with secondary education. In contrast to other world regions, postponement of successive births for extended periods accounted for much of the initial drop in fertility in these African countries. However, family size limitation by women with secondary education in Ethiopia and Kenya and longer birth spacing in Zimbabwe also played significant roles. Thus, birth control is being adopted in Eastern Africa in response to diverse changes in fertility preferences.

Objective: To explore the association between high-risk fertility behaviours and the likelihood of chronic undernutrition, anaemia and the coexistence of anaemia and undernutrition among women of reproductive age., Design: The 2011 Bangladesh Demographic and Health Survey, conducted from 8 July to 27 December 2011., Setting: Selected urban and rural areas of Bangladesh., Subjects: A total of 2197 ever-married women living with at least one child younger than 5 years. Exposure was determined from maternal reports of high-risk fertility behaviours. We considered three parameters, maternal age at the time of delivery, birth order and birth interval, to define the high-risk fertility behaviours. Chronic undernutrition, anaemia and the coexistence of anaemia and undernutrition among women were the outcome variables., Results: A substantial percentage of women were exposed to have a high-risk fertility pattern (41·8 %); 33·0 % were at single high-risk and 8·8 % were at multiple high-risk. After adjusting for relevant covariates, high-risk fertility behaviours were associated with increased likelihood of chronic undernutrition (adjusted relative risk; 95 % CI: 1·22; 1·03, 1·44), anaemia (1·12; 1·00, 1·25) and the coexistence of anaemia and undernutrition (1·52; 1·17, 1·98). Furthermore, multiple high-risk fertility behaviours appeared to have more profound consequences on the outcome measured., Conclusions: Maternal high-risk fertility behaviours are shockingly frequent practices among women in Bangladesh. High-risk fertility behaviours are important predictors of the increased likelihood of women's chronic undernutrition, anaemia and the coexistence of anaemia and undernutrition.

The analysis of fertility in colonizing populations is of great interest, since its individuals experience a major environmental change, and fertility rates can reflect the level of adaptation of the population to its new conditions. Using Northrop's genealogical compilations, this paper examines the fertility pattern of California's early Spanish-Mexican colonists between 1742 and 1876, their fitness levels and their trend across time throughout the colonizing period. A total of 197 women from 599 compiled families who had completed their reproductive period and had at least one child were analysed. The correlations among variables were also analysed in order to infer the relationship between longevity and fertility, and the influence of fertility determinants. The results show a natural fertility pattern, with a very young age at marriage and birth of first child (17.2 and 19.1 years respectively), and also a young age at last childbirth (38.8 years). The population's fitness showed greater values than for contemporary European populations, with 8 of 9.2 children surviving to adulthood, in comparison with 55% of newborns in Finland for the same period, suggesting a good adaptation of the population to their new environmental conditions. No relationship between fertility and lifespan was observed, as has been reported by other authors and in opposition to classical theories. A temporal trend in the number of children, consisting of three different phases, was observed, in accordance with the stability of living conditions in the region.

In life history theory, early life adversity is associated with an accelerated reproductive tempo. In harsh and unpredictable conditions in developing societies fertility is generally higher and the reproductive tempo faster than in more secure environments. This paper examines whether differences in female anthropometry, particularly adult height, are associated with fertility intentions of women in urban environments in India. The study population consists of women aged 15-29 (N=4485) in slums and non-slums of eight Indian cities in the National Family Health Survey (NFHS) of 2005-2006. Adult height is taken as a proxy for early childhood health and nutritional condition. Fertility intentions are examined by using two variables: the desire to have a child or another child, and to have it relatively soon, as indicative of accelerated reproductive scheduling. Evidence supporting the acceleration hypothesis is found in two urban frames out of 26 examined in a two-staged multinomial logistic model. In three cases, the relationship between fertility intentions and height is the opposite than expected by the acceleration hypothesis: taller women have a higher predictive probability of desiring a(nother) child and/or narrower birth spacing. Potential explanations for the partly contradictory relationship between the childhood health indicator and fertility intentions are discussed.

Particular features of human female life history, such as short birth intervals and the early cessation of female reproduction (menopause), are argued to be evidence that humans are 'cooperative breeders', with a reproductive strategy adapted to conditions where mothers receive substantial assistance in childraising. Evolutionary anthropologists have so far largely focussed on measuring the influence of kin on reproduction in natural fertility populations. Here we look at the effect in a present-day low-fertility population, by analysing whether kin affect parity progression in the British Household Panel Study. Two explanatory variables related to kin influence significantly increase the odds of a female having a second birth: i) having relatives who provide childcare and ii) having a larger number of frequently contacted and emotionally close relatives. Both effects were measured subject to numerous socio-economic controls and appear to be independent of one another. We therefore conclude that kin may influence the progression to a second birth. This influence is possibly due to two proximate mechanisms: kin priming through communication and kin assistance with childcare.

Based on historical data pertaining to the Krummhörn population (eighteenth and nineteenth centuries, Germany), we compared reproductive histories of mothers according to whether the maternal grandmother (MGM) or the paternal grandmother (PGM) or neither of them was resident in the parents' parish at the time of the mother's first birth. In contrast to effects of PGMs, we discovered conditional differences in the MGM's effects between landless people and wealthier, commercial farmers. Our data indicate that the presence of the MGM only lowers the woman's age at marriage (AAM) and her age at the birth of her first child (AFB) in the case of landless families. However, among commercial farmers, who can generally be characterized by a lower AAM and AFB, we found opposite tendencies for the MGM's effect leading to a relatively small delay in AAM and AFB. Moreover, we also analyzed differences in the completed fertility (i.e., children ever born: CEB). Results indicate that landless families in general do have fewer CEB compared with commercial farmers except for those families in which the MGM has been present. Emphasizing that the adaptiveness of investment decisions should depend on the interaction of genetic, lineage-specific (intrinsic) and ecologically imposed (extrinsic) constraints, we conclude that kin strategies consequently address different fitness components under different conditions.

To compensate for the high metabolic costs of lactation, the likelihood of re-impregnation shortly after childbirth is normally reduced due to hormonal changes triggered by breast feeding during the postpartum period. Nowadays, however, bottle feeding as a substitute for breast feeding precludes such changes and leads to early postpartum reinstatement of fertility. We suggest that recent data showing the risk of autism goes up dramatically as the time between pregnancies goes down [1] may be a byproduct of bottle feeding. The decision to bottle feed your last child may unwittingly put your next child at risk of being autistic., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Adverse pregnancy outcomes have long been observed to cluster within women resulting in the inclusion of past reproductive history in clinical assessments and perinatal scoring systems. However, limited study has focused on the clustering of fecundability as measured by time to pregnancy (TTP), despite growing evidence suggestive of a possible association with adverse pregnancy outcomes known to cluster within women. We sought to empirically evaluate the clustering of conception delay, and TTP more globally, in one of the few existing prospective pregnancy cohort studies that captured women's successive pregnancies. The study cohort comprised 544 women who contributed 1119 pregnancies in the U.S. Collaborative Perinatal Project. We used a discrete Cox frailty model to estimate the degree and significance of within-woman clustering of TTP. Women with an initial conception delay (TTP > 6 months) were older, less educated and had higher body mass indices than women not experiencing delays (TTP ≤ 6 months). Our analysis indicates that there is significant within-woman clustering of TTP (variance of the frailty = 0.80, [95% confidence interval 0.49, 1.11]) after adjusting for baseline maternal age, body mass index and education level. Similar to many other reproductive and perinatal outcomes, our findings suggest that TTP clusters within women. Identifying exposures or behaviours that affect TTP may offer strategies for reducing conception delay in future pregnancy attempts., (Published 2011. This article is a US Government work and is in the public domain in the USA.)

Background: Several embedded religious minority populations in the US have experienced fertilities consistent with natural fertility populations. In 1996, Wenger Mennonite total fertility reached 8.31., Aim: This study updates Wenger fertility through 2006, highlights regional differences in fertility and identifies factors that may contribute to continuing high fertility., Subjects and Methods: The Wengers are a religious minority who employ distinctive clothing, a rural farming lifestyle and limited use of technology. They publish a church directory every five years with detailed records of births, deaths and marriages. This directory was transformed into an SPSS database that allowed detailed analysis of fertility behaviour through 2006., Results: Wenger total marital fertility continues to be high (8.01). Wenger women have almost no premarital conceptions, do not marry until their early 20s, but achieve very high fertility immediately after they marry. Sharp differences exist among various settlements, with the highest fertilities in the newer Midwestern settlements., Conclusion: The Wengers continue to succeed in maintaining a distinct way of life and very high fertility in the midst of the larger US society. This fertility is tied to their high commitment to a rural farming way of life, strong community support and a pro-natalist ideology.

During the first few years of the Islamic Revolution of 1979, and aided by pro-natal government policies, Iranian fertility was on the rise. In a reversal of its population policy, in 1989, the government launched an ambitious and innovative family planning program aimed at rural families. By 2005, the program had covered more than 90% of the rural population and the average number of births per rural woman had declined to replacement level from about 8 births in the mid 1980s. In this paper, we evaluate the impact of a particular feature of the program - health houses - on rural fertility, taking advantage of the variation in the timing of their construction across the country. We use three different methods to obtain a range of estimates for the impact of health houses on village-level fertility: difference-in-differences (DID), matching DID, and length of exposure. We find estimates of impact ranging from 4 to 20% of the decline in fertility during 1986-1996., ((c) 2010 John Wiley & Sons, Ltd.)

Objective: To test, among an urban primarily African American sample, the effects of prenatal and infancy home visiting by nurses on mothers' fertility, partner relationships, and economic self-sufficiency and on government spending through age 12 years of their firstborn child., Design: Randomized controlled trial., Setting: Public system of obstetric and pediatric care in Memphis, Tennessee., Participants: A total of 594 urban primarily African American economically disadvantaged mothers (among 743 who registered during pregnancy). Intervention Prenatal and infancy home visiting by nurses., Main Outcome Measures: Mothers' cohabitation with and marriage to the child's biological father, intimate partner violence, duration (stability) of partner relationships, role impairment due to alcohol and other drug use, use and cost of welfare benefits, arrests, mastery, child foster care placements, and cumulative subsequent births., Results: By the time the firstborn child was 12 years old, nurse-visited mothers compared with control subjects reported less role impairment owing to alcohol and other drug use (0.0% vs 2.5%, P = .04), longer partner relationships (59.58 vs 52.67 months, P = .02), and greater sense of mastery (101.04 vs 99.60, P = .005). During this 12-year period, government spent less per year on food stamps, Medicaid, and Aid to Families with Dependent Children and Temporary Assistance for Needy Families for nurse-visited than control families ($8772 vs $9797, P = .02); this represents $12 300 in discounted savings compared with a program cost of $11 511, both expressed in 2006 US dollars. No statistically significant program effects were noted on mothers' marriage, partnership with the child's biological father, intimate partner violence, alcohol and other drug use, arrests, incarceration, psychological distress, or reports of child foster care placements., Conclusion: The program improved maternal life course and reduced government spending among children through age 12 years.

This study uses data from a population-based survey to examine the fertility schedules of 704 women in a rural district of Malawi. The main objective is to assess self-reported fecundity status as a measure of fertility impairment. Life tables are used to examine the timing and tempo of births for women reporting difficulty getting pregnant as compared to women with no reported fecundity difficulties. Results of the analysis indicate that women with self-reported fecundity difficulties are older at each birth and have longer median birth intervals than do women with no reported difficulties. Cox proportional hazards models show that the report of a difficulty getting pregnant is significantly associated with at least a 30% lower likelihood of a first, second, or third birth. The relationships are not modified when accounting for demographic characteristics, previous sexual behaviors, or STI status., (Am. J. Hum. Biol. 18:214-218, 2006. (c) 2006 Wiley-Liss, Inc.)

Women born at different periods within the 20th century in England and Wales have followed varying fertility pathways with large changes in, for example, proportions having no children or only one child. Among the consequences of these changes may be effects on women's health later in life. Links between fertility histories and later health and mortality have been investigated in several studies, but in many of these socio-economic characteristics have not been allowed for, even though there are socio-economic differences in both fertility and mortality patterns and results are conflicting. Here we analyse associations between the fertility histories of women born 1911-1940 in England and Wales and their mortality and health status after age 50. We used data from the Office for National Statistics Longitudinal Study; a record linkage study of approximately 1% of the population initially based on those enumerated in the 1971 Census of England and Wales. We used survival analysis to investigate the effects of parity, short birth intervals, and timing of fertility on mortality from age 50 to the end of 2000, controlling for a range of relevant socio-demographic characteristics. For survivors to 1991, we additionally used logistic regression to model probability of having a limiting long-term illness in 1991. We found that nulliparous women and women with five or more children had significantly higher mortality than other women, and that in the oldest groups women with just one child also had raised mortality. Women who had been teenage mothers had higher mortality and higher odds of poor health than other parous women. Mothers with short birth intervals, including mothers of twins, also had elevated risks in some cohorts. Late childbearing (after age 39) was associated with lower mortality. Personal demographic history is an important factor to consider in analyses of health and mortality variations in later life. More research is needed to further elucidate causal pathways.

Four weeks before their predicted mean second lactation calving date, 60 spring-calving Holstein-Friesian cows were blocked into groups of six on the basis of their predicted calving date and body condition score, and allocated at random to one of six dietary treatments in a factorial design: ad libitum grass silage, ad libitum grass silage plus barley straw or ad libitum grass silage plus 3 kg of concentrates, was offered for four weeks before the expected calving date, and after calving they were offered either 4 kg or 8 kg of concentrates plus ad libitum grass silage for eight weeks. On average, the first luteal activity occurred in all the groups at 29 days after calving. Seventeen of the cows had an atypical first plasma progesterone profile; 12 were anovulatory, three had prolonged luteal phases and two became anovulatory after having been cyclic. The cows offered grass silage only before calving had a significantly shorter mean (se) interval between calving and second luteal activity (44.9 [2.1] days), than the cows offered grass silage and straw (53.5 [1.9] days) or grass silage and concentrates (51.5 [3.2] days) (P<0.05). After calving none of the 28 cows offered grass silage and 4 kg of concentrates started cycling before day 21, whereas five of the 30 cows offered grass silage and 8 kg of concentrates cycled before day 21 (P<0.05).

We model the impact of past migration on fertility, assessing the separate effects of relative urbanization of the destination, as a proxy for norms, and post-migration employment, as a proxy for opportunity costs. In the Philippines, we find that large fertility declines accompany post-migration employment. If not followed by work for pay, the estimated fertility impact of migration is small. We find little evidence of migrant selectivity in fertility, and offer speculative evidence that fertility disruption accompanying migration may be large enough to account for much of the apparent effect of normative adaptation.

The large human brain, the long period of juvenile dependence, long life span, and male support of reproduction are the co-evolutionary result of the human niche based on skill-intensive techniques of resource accrual. The regulation of fertility under traditional conditions is based upon a co-evolved psychology and physiology where adjustments of investment in offspring depend upon the returns to skill and mortality hazards. When all wealth is somatic, the hormonal system controlling ovulation and implantation translates income into genetic descendants. In modern society the existence of extra-somatic wealth is a critical condition to which our evolved proximate physiological mechanisms do not respond. However, psychological mechanisms regulating parental investment in offspring quality may lead to greater and greater investment in own and offspring education, a smaller desired family size, a delay in the onset of reproduction, and a reduction in the total numbers of offspring produced. This delay in reproduction can cause many individuals to produce fewer children than desired because fecundity falls during the reproductive part of the life course. As more individuals in a society follow this pattern, more will fail to reach their desired family size. At the same time the effective use of birth control decreases the numbers of families producing more children than desired. Below replacement fertility can result. Predictions from this model were tested using data from the National Survey of Families and Households and the Albuquerque Men study.

Polygyny can increase, decrease, or have no effect on fertility. Understanding how this can occur requires consideration of both the proximate determinants of fertility and the ultimate effects of polygyny as a female reproductive strategy. Several factors reduced the fertility of polygynous women in 19th century Utah, including marrying at an older age, marrying older men, and conflict between co-wives. Sterility did not explain the reduced number of children in polygynous women, nor is there evidence of a "dilution effect" from sharing a husband. If women could anticipate a reduction in their own fertility, why would they still choose polygyny? Evidence suggests that they chose it because the children of polygynous men had increased fertility, high enough to offset the low fertility of polygynous women themselves.

This paper analyses the behavioural effects of infant and child mortality on birth intervals in Kenya. Analysing the behavioural effects of infant and child mortality on fertility independent of its biological effects has been considered a difficult task. In this paper, a procedure for analysing these effects separately is developed and applied to the 1989 Kenya Demographic and Health Survey (KDHS) data. The results of the analysis suggests that women in Kenya adopt various strategies such as curtailing the duration of breastfeeding, increasing frequency of coitus, and to a lesser extent use of contraception in order to replace infant or children who have died or to insure against those who are likely to die. These findings suggest the existence of behavioural effects of infant and child mortality on fertility in Kenya.

"Helpers at the nest," usually offspring of a preceding litter who contribute by feeding the young to increase the reproductive success of a breeding pair, are known in many species of birds and mammals. Although similar behaviors were described by ethnological observations in several human societies, there is a lack of data on their existence and role. This study of 794 reproductive life histories of post-menopausal Berber women of Southern Morocco aims to provide such information. Results show that the presence of "probable helpers" in the household is related to higher fertility scores and is associated with improved survival of offspring to sexual maturity. In contrast to sparse observations from other human societies, there is no indication that child caretaking would be specific to eldest daughters. Although the association between offspring survival and helping patterns seems highly probable, there is no confirmation that child caretaking per se is the relevant variable. Contrary to nonhuman helpers at the nest, workloads of children range from housekeeping to light agricultural tasks, and are not focused on assisting younger siblings. The improvement of reproductive success is probably the result of multiple interactions, among which the network of kinship would play a role at both the levels of economy and reciprocal assistance.

The fertility pattern, in terms of birth intervals, in a rural population not practicing contraception belonging to La Alta Alpujarra Oriental (southeast Spain) is analyzed. During the first half of the 20th century, this population experienced a considerable degree of geographical and cultural isolation. Because of this population's high variability in fertility and therefore in birth intervals, the analysis was limited to a homogenous subsample of 154 families, each with at least five pregnancies. This limitation allowed us to analyze, among and within families, effects of a set of variables on the interbirth pattern, and to avoid possible problems of pseudoreplication. Information on birth date of the mother, age at marriage, children's birth date and death date, birth order, and frequency of miscarriages was collected. Our results indicate that interbirth intervals depend on an exponential effect of maternal age, especially significant after the age of 35. This effect is probably related to the biological degenerative processes of female fertility with age. A linear increase of birth intervals with birth order within families was found as well as a reduction of intervals among families experiencing an infant death. Our sample size was insufficient to detect a possible replacement behavior in the case of infant death. High natality and mortality rates, a secular decrease of natality rates, a log-normal birth interval, and family-size distributions suggest that La Alpujarra has been a natural fertility population following a demographic transition process.

In Bangladesh, the total fertility rate declined from more than six children per woman of reproductive age in 1980 to 3.3 children per woman in 1996. Much discussion has ensued about the circumstances responsible for this decline and, in particular, about the contribution made by the national family planning program. For this study, qualitative interviews were conducted with 67 women concerning the factors influencing their reproductive behavior. The participants, residents of a rural area in southwestern Bangladesh, consisted of two groups: women who were currently practicing family planning and women who had never practiced or had not done so for at least four years. The findings suggest that the family planning program has played an important role in reducing family size, but also indicate that economic and social changes, and especially growing aspirations (particularly for a life outside agriculture) have combined with changes in the nature of family decision making to make couples more receptive to the idea of family planning.

Using Demographic and Health Survey data from 20 sub-Saharan African countries, this article compares the actual lengths of birth intervals to women's reported preferred lengths, and assesses the implications of the difference between the two for selected demographic and health indicators. The results show a clear pattern. In Comoros, Ghana, Kenya, Rwanda, and Zimbabwe, women prefer much longer birth intervals than those they actually have, compared with women in the other 15 countries studied. As a consequence, the potential effects of spacing preferences on the level of fertility and on the prevalences of short (less than 24 months) birth intervals and child malnutrition are greatest in the same five countries. The covariates of preferred birth-interval lengths are also examined. An explanation is offered for this pattern, based on the observed sharp decline in fertility recently experienced by these five "forerunners." In general, women who know, approve of, discuss, and use family planning prefer longer intervals than do their counterparts. The policy and program relevance of these results is discussed.

There is a general consensus in the literature that fertility differences between populations can be accounted for by differences in just four key proximate determinants: nuptiality, the postpartum non-susceptible period, contraception and abortion. Natural fecundibility is generally assumed to be constant between populations. This paper puts the theoretical and empirical case for a re-evaluation of that assumption, drawing on the under-utilized data on sexual activity collected in the Demographic Health Surveys (DHSs). Using data for married women in nine African countries, the analysis finds substantial population level differences in mean monthly coital frequency, which, if accurate, suggest an important demographic effect. There is a clear regional patterning to these differences, with levels of activity considerably lower among women in the West African populations included in the study than those from East and southern Africa. For West Africa in particular the data indicate the normality of exceptionally long periods of very infrequent or no intercourse by married women outside the period of postpartum abstinence. The findings challenge prevailing presumptions concerning susceptibility to pregnancy in marriage on which statistics for unmet need for family planning are derived. While doubts are raised over the precision of the sexual activity data used, the paper argues for the need for a greater effort to operationalize the 'proximate determinant of conception', not only for more accurate fertility modelling, but also as a planning tool for a more sensitive provision of family planning services in Africa.

This paper analyzes the age pattern of effective fecundability from populations with no evidence of deliberate fertility control using a new convolution model of fecundability. The analysis is based on a sample of Hutterite birth histories from the mid-20th century, and birth histories of French Canadians from the 17th and 18th centuries. The main findings are as follows: 1) the level of effective fecundability is higher among the French Canadians compared to the Hutterites; 2) effective fecundability peaks at age 20 for the Hutterites, and in the early to mid-20s for the French Canadians; 3) Hutterite effective fecundability declines almost linearly from age 20 to 45, and French Canadian effective fecundability declines slowly from its peak to the early 30s, and more rapidly at older ages; and 4) the duration of postpartum amenorrhea is longer for the French Canadians than for the Hutterites. Because of the shorter periods of postpartum amenorrhea the Hutterites have about the same average number of children as the French Canadians, even though the French Canadians have higher effective fecundability.

In an historical cohort study, we compared the reproductive performances of women born after short (< 14 completed months), intermediate (21-32 completed months), and long (> 39 completed months) birth intervals. Of the initial study base, comprising family reconstitutions of 1,425 women born between 1873 and 1902 in or around Rotterdam (The Netherlands) and married before age 45, a large portion (data of 1,001 women born between 1888 and 1902) was uninformative because of (unintended) selection on birth control behavior. Among the remaining 424 women, those born after very short birth intervals (less than 1 year) showed higher likelihood of childlessness and stillbirth in the offspring than those born after intermediate intervals (adjusted odds ratios (OR) and 95%-confidence intervals: 7.7 [1.8-33.0] and 3.3 [1.3-8.3], respectively). The latter association, however, nearly disappeared after restriction to women whose preceding sibling lived at least 1 year. Women born after modestly short intervals (12-13 months) exhibited longer interpregnancy intervals. So did women born after long birth intervals, but this might well be attributable to intergenerational transmission of reproductive behavior. These results indicate that fecundability is reduced in women born after short birth intervals.

Censuses and surveys frequently collect information on period fertility through questions on the timing of last births. The standard approach to estimating fertility with open-interval data uses the proportion of women giving birth in the year before the interview. I propose a more efficient, maximum likelihood method for estimating fertility from open-interval data. I illustrate a mathematical derivation of the new method, perform sensitivity analyses, and conduct empirical tests with Brazilian census data. The new estimators have small biases and lower variance than standard estimators for open-interval data. Consequently, the new method is more likely to generate accurate results from small or moderately sized samples.

The purpose of this paper is to demonstrate a causal approach to interdependent systems based on two empirical investigations. These examples demonstrate 1) the study of two highly interdependent processes: entry into first marriage as the dependent process and the process of first birth/first pregnancy as the explaining one; 2) an interdependence occurring mainly in a very specific phase of individuals' lives (i.e., during the period of first family formation); 3) the involvement of time lags between cause and its effect (e.g., time until detection of conception); and 4) the highly dynamic character of an unfolding effect over time (i.e., the effect of first pregnancy/first birth on first marriage strongly depends on the progress of pregnancy and the time since the birth has taken place).

Objective: To assess the effect of psychological distress on time to first pregnancy., Design: A follow-up study of time to pregnancy with prospective data on distress, with controlling for potential confounding variables., Setting: Two university hospitals., Patient(s): Danish couples (n = 430) who were planning their first pregnancy and had no previous reproductive experience were followed for six menstrual cycles. Psychological distress was measured in each menstrual cycle by the General Health Questionnaire., Intervention(s): None., Main Outcome Measure(s): A clinically recognized pregnancy or a biochemical pregnancy detected in urine samples from each period of vaginal bleeding., Result(s): For cycles with the highest distress score (General Health Questionnaire score >80th percentile), the probability of conception per cycle was 12.8%, compared with 16.5% in other cycles (adjusted odds ratio [OR] 0.6; 95% confidence interval [CI] 0.4-1.0). The effect of distress was found almost exclusively among women with long menstrual cycles (OR 0.1; 95% CI 0.01-0.4 and OR 0.9; 95% CI 0.5-1.4 for women with cycles of > or =35 and <35 days, respectively). An increased incidence of early embryonal loss was also found among highly distressed women with long cycles, but was based on a small number of observations., Conclusion(s): Psychological distress may be a risk factor for reduced fertility in women with long menstrual cycles.

The status of women, which is relative and multidimensional, has an important bearing on any long-term reduction in fertility. In Indian society, where cohabitation and childbearing are socially sanctioned only after marriage, the length of the first-birth interval affects the completed family size by influencing the spacing and childbearing pattern of a family. This study examines the influence of certain aspects of the status of married women--education, employment, role in family decision making, and age at marriage--along with three socioeconomic variables--per capita income of the family, social position of the household, and the caste system--on the duration of the first-birth interval in an urban Hindu society of the north-east Indian state of Assam. The data were analysed by applying life table and hazard regression techniques. The results indicate that a female's age at marriage, education, current age, role in decision making, and the per capita income of the household are the main covariates that strongly influence the length of the first-birth interval of Hindu females of urban Assam. Of all the covariates studied, a female's education appears to be a key mediating factor, through its influence on her probability of employment outside the home and thereby an earned income and on her role in family decision making. Unlike other Indian communities, the effect of the caste system does not have a significant effect on first-birth timing in this urban Hindu society.

This paper revisits and extends an inquiry on the age-at-menarche differential fecundity hypothesis. Earlier studies have interpreted the difference in the onset of female pubertal maturation as indicative of biological differences in fecundity between early and late menarcheal women. Using the WFS data for Sudan, the authors address the entire reproductive life of the women in terms of their transition from one parity to the next, as well as the speed with which birth intervals are closed, as a way to infer biological fecundity among the women. The study concludes that there is little evidence that early menarcheal women are more fecund than their late puberty counterparts.

Surprisingly little is known about the mechanisms that underlie variation in female fertility in humans. Data on this topic are nonetheless vital to a number of pragmatic and theoretical enterprises, including population planning, infertility treatment and prevention, and evolutionary ecology. Here we study female fertility by focusing on one component of the interbirth interval: the waiting time to conception during menstrual cycling. Our study population is a Dogon village of 460 people in Mali, West Africa. This population is pronatalist and noncontracepting. In accordance with animist beliefs, the women spend five nights sleeping at a menstrual hut during menses. By censusing the women present at the menstrual huts in the study village on each of 736 consecutive nights, we were able to monitor women's conception waits prospectively. Hormonal profiles confirm the accuracy of the data on conception waits obtained from the menstrual hut census (Strassmann [1996], Behavioral Ecology 7:304-315). Using survival analysis, we identified significant predictors of the waiting time to conception: wife's age (years), husband's age (< 35, 35-49, > 49 years), marital duration (years), gravidity (number of prior pregnancies), and breast-feeding status. Additional variables were not significant, including duration of postpartum amenorrhea, sex of the last child, nutritional status, economic status, polygyny, and marital status (fiancée vs. married). We fit both continuous and discrete time survival models, but the former appeared to be a better choice for these data.

Effects on reproduction in a total of 135 dairy cows managed for calving intervals of 12, 15 or 18 months (72, 38 and 25 cows respectively) were studied. The cows were of the Swedish Red and White Breed (SRB) and the Swedish Freisian Breed (SLB) and were housed in 2 different herds with 3 different management systems (tied, loose, and tied but milked in a milking parlour; mixed). The cows in one of the herds (48 cows) were assigned for milking either 2 times or 3 times a day. When comparing conception rate at 1st insemination (AI) and the percentage of cows finally pregnant, we found no significant differences between the 3 calving interval groups, however, a tendency for a higher conception rate with a 15 months' interval compared with a 12 months' interval was found in one of the herds (50% vs 41.5%). The percentage of finally pregnant animals varied between 81% and 100%, but this variation was mainly attributed to the herd rather than calving interval group. A significantly higher percentage of cows was treated for anoestrous in the 12-month group than in the 15-month group in one of the herds (28.6% vs. 5.3%). The frequency of ovulations with external heat signs increased with ovulation number up to the 4th ovulation and thereafter remained stable. No significant difference was found in number of AIs required per conception with respect to calving intervals, breeds, or milking frequency groups. However, cows milked 3 times a day had a significantly longer interval from the 1st AI to conception compared with cows milked 2 times a day (45.8 days vs 17.6 days, p < .01). Cows kept loose exhibited 1st ovulatory oestrous, approximately 2 weeks earlier (55.9 days vs 69.7 days, p < .05) than their herd mates kept tied. In conclusion, our study shows that lengthening the calving interval to 15 or 18 months may have a positive influence on reproduction in terms of less need for treatments of ovarian disorders and higher conception rates. Our results also indicate that milking 3 times a day may have negative effects, and keeping cows in a loose-housing management system may have positive effects on ovarian function.

The literature on the effect of fertility on child survival is extensive especially since the accumulation of data from the World Fertility, and Demographic and Health Surveys. Comparatively, empirical studies examining the other side of the relationship--the effect of child survival on fertility--are sparse although theoretical considerations suggest the interdependence of child survival and fertility. Furthermore, the relationship of child survival and fertility is often examined at the micro-level. There is growing recognition, however, that this relationship may be also influenced by macro-level factors. This study attempts to measure the effect of child survival on birth intervals in Zimbabwe using a micro-macro analytical approach based on the individual and community data from the 1988 Zimbabwe Demographic and Health Survey, and the 1989/1990 Zimbabwe Service Availability Survey, respectively. The multivariate analysis showed that there is a replacement effect in the relationship between child survival and fertility independent of individual characteristics of women in Zimbabwe. The analysis also showed that health interventions as measured by coverage and visit by a mobile family planning clinic, and access to a health service have differential impact on fertility in Zimbabwe controlling for the survival status of the previous to the last child and individual characteristics of the women.

In almost all mammals lactation, or more correctly the suckling stimulus, induces a period of infertility designed to provide the optimal birth spacing for survival of the offspring. The duration of lactational infertility depends on the sucking activity of the young with little evidence to support a role for nutritional status. Suckling disrupts the normal pulsatile pattern of hypothalamic gonadotrophin releasing hormone (GnRH)2 secretion resulting in reduced LH secretion from the pituitary. Secretion of FSH returns to its normal cyclic pattern early in lactation and ovarian follicles may develop under its influence. However, until suckling declines, the follicles fail to secrete amounts of estradiol adequate to stimulate an LH surge and ovulation. The suckling stimulus may affect GnRH secretion by affecting prolactin, opiate and dopaminergic tone in the hypothalamus but no unifying mechanism has yet been proposed convincingly. The birth spacing effects of breastfeeding in women have a profound effect on infant well-being, and breastfeeding still prevents more pregnancies than all forms of artificial contraception.

"Many authors [have] pointed out that analysis of open birth interval (the period elapsed from the last live birth till the date of the survey) could be of great interest to study the process of human reproduction, because it directly exhibits changes in fertility due to recent use of contraception or incidence of secondary sterility. Moreover, open birth intervals may be chosen to study the linkage between fertility and migration. A probability model for describing variations in the length of open birth intervals has been applied separately to couples with both spouses present at home, and to couples with one spouse having migrated away. The model has then been applied to [survey data for India] to get an estimate of the risk of conception and of secondary sterility." (SUMMARY IN ITA AND FRE), (excerpt)