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Familial correlations in birth weight and gestational age have been explained by fetal and maternal genetic factors, mainly in studies on offspring of twins. The aim of the present intergenerational study was to estimate and compare fetal and maternal genetic effects and shared sibling environmental effects on birth weight and gestational age and also on crown-heel length and head circumference. The authors used path analysis and maximum likelihood principles to estimate these effects and, at the same time, to adjust for covariates. Parent-offspring data were obtained from the Medical Birth Registry of Norway from 1967 to 2004. For the analysis of birth weight and crown-heel length, 101,748 families were included; for gestational age, 91,617 families; and for head circumference, 77,044 families. Assuming no cultural transmission and random mating, the authors found that fetal genetic factors explained 31% of the normal variation in birth weight and birth length, 27% of the variation in head circumference, and 11% of the variation in gestational age. Maternal genetic factors explained 22% of the variation in birth weight, 19% of the variation in birth length and head circumference, and 14% of the variation in gestational age. Relative to the proportion of explained variation, fetal genes were most important for birth length and head circumference. [ABSTRACT FROM AUTHOR]

Objectives: To examine trends in the prevalence of congenital heart defects (CHDs) in Europe and to compare these trends with the recent decrease in the prevalence of CHDs in Canada (Quebec) that was attributed to the policy of mandatory folic acid fortification., Study Design: We used data for the period 1990-2007 for 47 508 cases of CHD not associated with a chromosomal anomaly from 29 population-based European Surveillance of Congenital Anomalies registries in 16 countries covering 7.3 million births. We estimated trends for all CHDs combined and separately for 3 severity groups using random-effects Poisson regression models with splines., Results: We found that the total prevalence of CHDs increased during the 1990s and the early 2000s until 2004 and decreased thereafter. We found essentially no trend in total prevalence of the most severe group (group I), whereas the prevalence of severity group II increased until about 2000 and decreased thereafter. Trends for severity group III (the most prevalent group) paralleled those for all CHDs combined., Conclusions: The prevalence of CHDs decreased in recent years in Europe in the absence of a policy for mandatory folic acid fortification. One possible explanation for this decrease may be an as-yet-undocumented increase in folic acid intake of women in Europe following recommendations for folic acid supplementation and/or voluntary fortification. However, alternative hypotheses, including reductions in risk factors of CHDs (eg, maternal smoking) and improved management of maternal chronic health conditions (eg, diabetes), must also be considered for explaining the observed decrease in the prevalence of CHDs in Europe or elsewhere., (Copyright © 2013 Mosby, Inc. All rights reserved.)

Background: Maternal pregestational diabetes is a well-known risk factor for congenital anomalies. This study analyses the spectrum of congenital anomalies associated with maternal diabetes using data from a large European database for the population-based surveillance of congenital anomalies., Methods: Data from 18 population-based EUROCAT registries of congenital anomalies in 1990-2005. All malformed cases occurring to mothers with pregestational diabetes (diabetes cases) were compared to all malformed cases in the same registry areas to mothers without diabetes (non-diabetes cases)., Results: There were 669 diabetes cases and 92,976 non diabetes cases. Odds ratios in diabetes pregnancies relative to non-diabetes pregnancies comparing each EUROCAT subgroup to all other non-chromosomal anomalies combined showed significantly increased odds ratios for neural tube defects (anencephaly and encephalocele, but not spina bifida) and several subgroups of congenital heart defects. Other subgroups with significantly increased odds ratios were anotia, omphalocele and bilateral renal agenesis. Frequency of hip dislocation was significantly lower among diabetes (odds ratio 0.15, 95% CI 0.05-0.39) than non-diabetes cases. Multiple congenital anomalies were present in 13.6 % of diabetes cases and 6.1 % of non-diabetes cases. The odds ratio for caudal regression sequence was very high (26.40,95% CI 8.98-77.64), but only 17% of all caudal regression cases resulted from a pregnancy with pregestational diabetes., Conclusions: The increased risk of congenital anomalies in pregnancies with pregestational diabetes is related to specific non-chromosomal congenital anomalies and multiple congenital anomalies and not a general increased risk., (Copyright © 2012 Wiley Periodicals, Inc.)

Background: Environmental factors influencing the developmental origins of health and disease need to be identified and investigated. In utero exposure to tobacco smoke has been associated with obesity and a small increase in blood pressure in children; however, whether there is a corresponding increased risk of conditions such as diabetes and hypertension during adulthood remains unclear., Objective: Our goal was to assess the association of self-reported in utero exposure to tobacco smoke with the prevalence of obesity, hypertension, type 2 diabetes mellitus (T2DM), and gestational diabetes mellitus (GDM) in women 14-47 years of age., Methods: We conducted a cross-sectional analysis of the Norwegian Mother and Child Cohort Study, which enrolled pregnant women in Norway from 1999 thorough 2008. Exposure to tobacco smoke in utero (yes vs. no) was ascertained on the baseline questionnaire (obtained at ~ 17 weeks' gestation); the outcomes were ascertained from the Medical Birth Registry of Norway and the questionnaire. Our analysis included 74,023 women., Results: Women exposed to tobacco smoke in utero had 1.53 times the odds of obesity [95% confidence interval (CI): 1.45, 1.61] relative to those unexposed, after adjusting for age, education, and personal smoking. After further adjustment for body mass index, the odds ratio for hypertension was 1.68 (95% CI: 1.19, 2.39); for T2DM 1.14 (95% CI: 0.79, 1.65); and for GDM 1.32 (95% CI: 1.10, 1.58) among exposed compared with unexposed., Conclusions: Exposure to tobacco smoke in utero was associated with obesity, hypertension, and GDM in adult women. The possibility that the associations were attributable to unmeasured confounding cannot be excluded.

Objective: To estimate intergenerational recurrence risk of prolonged and post-term gestational age., Design: Population-based cohort study., Setting: Norway, 1967-2006., Population: Intergenerational data from the Medical Birth Registry of Norway of singleton mothers and fathers giving birth to singleton children: 478 627 mother-child units and 353 164 father-child units. A combined mother-father-child file including 295 455 trios was also used., Methods: Relative risks were obtained from contingency tables and relative risk modelling., Main Outcome Measures: Gestational age ≥41 weeks (≥287 days), ≥42 weeks (≥294 days) and ≥43 weeks (≥301 days) of gestation in the second generation., Results:   A post-term mother (≥42 weeks) had a 49% increased risk of giving birth to a child at ≥42 weeks (relative risk [RR] 1.49, 95% CI 1.47-1.51) and a post-term father had a 23% increased risk of fathering a child at ≥42 weeks (RR 1.23, 95%CI 1.20-1.25). The RRs for delivery at ≥41 weeks were 1.29 (1.28-1.30) and 1.14 (1.13-1.16) for mother and father, respectively, and for ≥43 weeks 1.55 (1.50-1.59) and 1.22 (1.17-1.27). The RR of a pregnancy at ≥42 weeks in the second generation was 1.76 (1.68-1.84) if both mother and father were born post-term. Adjustment for maternal age in both generations, fetal sex in the second generation, parity, and maternal and paternal birthweight did not influence the risk estimates., Conclusions: There is a familial factor related to recurrence of prolonged pregnancy across generations and both mother and father seem to contribute., (© 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2011 RCOG.)

Objective: The objective of this study was to compare international trends in pre-eclampsia rates and in overall pregnancy hypertension rates (including gestational hypertension, pre-eclampsia and eclampsia)., Design: Population data (from birth and/or hospital records) on all women giving birth were available from Australia (two states), Canada (Alberta), Denmark, Norway, Scotland, Sweden and the USA (Massachusetts) for a minimum of 6 years from 1997 to 2007. All countries used the 10th revision of the International Classification of Diseases, except Massachusetts which used the 9th revision. There were no major changes to the diagnostic criteria or methods of data collection in any country during the study period. Population characteristics as well as rates of pregnancy hypertension and pre-eclampsia were compared., Results: Absolute rates varied across the populations as follows: pregnancy hypertension (3.6% to 9.1%), pre-eclampsia (1.4% to 4.0%) and early-onset pre-eclampsia (0.3% to 0.7%). Pregnancy hypertension and/or pre-eclampsia rates declined over time in most populations. This was unexpected given that factors associated with pregnancy hypertension such as pre-pregnancy obesity and maternal age are generally increasing. However, there was also a downward shift in gestational age with fewer pregnancies reaching 40 weeks., Conclusion: The rate of pregnancy hypertension and pre-eclampsia decreased in northern Europe and Australia from 1997 to 2007, but increased in Massachusetts. The use of a different International Classification of Diseases coding version in Massachusetts may contribute to the difference in trend. Elective delivery prior to the due date is the most likely explanation for the decrease observed in Europe and Australia. Also, the use of interventions that reduce the risk of pregnancy hypertension and/or progression to pre-eclampsia (low-dose aspirin, calcium supplementation and early delivery for mild hypertension) may have contributed to the decline.

Objective: To investigate the relationship between maternal preterm birth and fetal growth in one generation and perinatal mortality of twin offspring in the next generation., Design: Population-based cohort study., Setting: The Medical Birth Registry of Norway from 1967 to 2008., Population: Linked generational data with 9426 mother-twin pair units., Methods: Twin offspring were linked to their mothers by means of the unique national identification numbers., Main Outcome Measures: Perinatal mortality in twin offspring., Results: The twin prevalence was not dependent on the mother's gestational age at birth, but increased with increasing birthweight in term mothers. Maternal gestational age was strongly and inversely associated with a risk of perinatal death in one or both of her twin offspring. Compared with term mothers, preterm mothers born at 27-31 and 32-34 weeks had relative risks (RRs) for perinatal loss of 3.83 [95% confidence interval (CI), 1.56-9.36] and 2.41 (95% CI, 1.29-4.50), respectively. This effect was even stronger after the use of assisted reproductive technologies (ART), with a significant interaction between maternal gestational age and ART (P = 0.03). Further, term mothers with birthweight-by-gestational age Z-scores of -2 or less had more than twice the risk of a perinatal loss in their twin offspring relative to mothers with the most favourable birthweight Z-scores (1-1.99) [RR, 2.42 (95% CI, 1.37-4.29)]., Conclusions: Women born preterm had an increased risk of perinatal mortality in their twin offspring, particularly after ART treatment. The same was true for women who were growth restricted at term. A twin pregnancy is a high-risk pregnancy in general, but even more so if the mother herself was born preterm or was growth restricted at birth., (© 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2011 RCOG.)

Knowledge of stillbirth recurrence risk is of clinical interest and may give etiological insight. The authors studied "gestational age-" and "weight-by-gestation-specific" stillbirth recurrence, and evaluated time trends in a population-based cohort study from the Medical Birth Registry of Norway, from 1967 to 2004. Singleton births, including stillbirths from 20 weeks' gestation, were linked to their mothers by national identification numbers. Stillbirth rates in second pregnancies among mothers with (N = 5,091) and without (N = 562,057; the reference group) a stillbirth in first pregnancies were compared across 4 gestational age and 3 weight-by-gestation groups. A remarkable symmetric pattern of gestational age-specific recurrence of stillbirth was found, with highest odds of stillbirth in the same age group. The adjusted odds ratio values associated with preterm stillbirth recurrence were high, for example, 25.7 (95% confidence interval: 19.8, 33.3) for stillbirth at 20-27 weeks' gestation (73/1,511 vs. 1,021/562,057), while lower for term stillbirth: adjusted odds ratio = 2.3 (95% confidence interval: 1.2, 4.7) (9/1,844 vs. 1,021/538,499). The proportion of second early stillbirths in the population attributable to previous early stillbirth was 6.4%, compared with 0.5% for second term stillbirth. Over time, recurrence of early stillbirth decreased, whereas that of mid/late stillbirth did not change significantly. A symmetric pattern of recurring stillbirth in similar weight-by-gestation groups was not found.

Background: The aim of this study was to examine trends of Down syndrome (DS) in relation to maternal age and termination of pregnancies (ToP) in 20 registries of the International Clearinghouse for Birth Defects Surveillance and Research (ICBDSR)., Methods: Trends of births with DS (live-born and stillborn), ToP with DS, and maternal age (percentage of mothers older than 35 years) were examined by year over a 12-year period (1993-2004). The total mean number of births covered was 1550,000 annually., Results: The mean percentage of mothers older than 35 years of age increased from 10.9% in 1993 to 18.8% in 2004. However, a variation among the different registers from 4-8% to 20-25% of mothers >35 years of age was found. The total mean prevalence of DS (still births, live births, and ToP) increased from 13.1 to 18.2/10,000 births between 1993 and 2004. The total mean prevalence of DS births remained stable at 8.3/10,000 births, balanced by a great increase of ToP. In the registers from France, Italy, and the Czech Republic, a decrease of DS births and a great increase of ToP was observed. The number of DS births remained high or even increased in Canada Alberta, and Norway during the study period., Conclusions: Although an increase in older mothers was observed in most registers, the prevalence of DS births remained stable in most registers as a result of increasing use of prenatal diagnostic procedures and ToP with DS., (2010 Wiley-Liss, Inc.)

There is increasing interest in the associations between parental birthweight and gestational age with their perinatal outcomes. We investigated perinatal mortality risk in offspring in relation to maternal and paternal gestational age and birthweight. We used population-based generational data from the Medical Birth Registry of Norway, 1967-2006. Singletons in both generations were included, forming 520,794 mother-offspring and 376,924 father-offspring units. Perinatal mortality in offspring was not significantly associated with paternal gestational age or birthweight, whereas it was inversely associated with maternal gestational age. A threefold increased risk in perinatal mortality was found among offspring of mothers born at 28-30 weeks of gestation relative to offspring of mothers born at term (37-43 weeks) (relative risk: 2.9, 95% CI 1.9, 4.6). There was also an overall association between maternal birthweight and offspring perinatal mortality. Relative risk for mothers whose birthweight was <2000 g was 1.5 (95% CI 1.1, 1.9), relative to mothers whose birthweight was 3500-3999 g. However, confined to mothers born at >or=34 weeks of gestation, the birthweight association was not significant. Weight-specific perinatal mortality in offspring was dependent on the birthweight of the mother and the father, that is, offspring who were small relative to their mother's or father's birthweight had increased perinatal mortality. In conclusion, a mother's gestational age, and not her birthweight, was significantly associated with perinatal mortality in the offspring, while there was no such association for the father.

Objective: To estimate whether a history of fetal growth restriction, abruptio placentae, preeclampsia, or live preterm birth is associated with excess risk of stillbirth in a subsequent pregnancy. We also estimated the maternal and paternal contributions to such effects., Methods: This was a population-based cohort study from 1967 to 2005. Pairs of first and second, second and third, third and fourth, and fourth and fifth births were identified among all births from the Medical Birth Registry of Norway; 747,221 pairs with the same parents, 51,708 with the same mother and different father, and 65,602 with the same father and different mother. The associations of gestational age categories (22-27, 28-32, 33-36, and at or above 37 weeks), small for gestational age (SGA), preeclampsia, and abruptio placenta in the first pregnancy with stillbirth and late abortion in the second were assessed by odds ratios (ORs) obtained by logistic regression., Results: The baseline rate of stillbirth during the study period was 1.0% of all births from 16 weeks of gestation. After births with gestational age 22-27, 28-32, and 33-36 weeks of gestation, stillbirth was six, three and two times more likely to occur than after a term birth (OR 5.7, 95% confidence interval [CI] 4.2-7.6; OR 2.6, 95% CI 2.1-3.3; and OR 1.7, 95% CI 1.5-1.9, respectively). Odds ratios of stillbirth subsequent to pregnancies with SGA, preeclampsia, and abruptio placentae were 1.7 (95% CI 1.6-1.9), 1.6 (95% CI 1.5-1.9), and 2.8 (95% CI 2.2-3.5), respectively, and increased with severity of the conditions. Gestational age below 33 weeks with preeclampsia or SGA carried 6-9 and 6-13-fold effects on later stillbirth, respectively. Men who fathered a pregnancy with preterm preeclampsia were significantly more likely to father a stillbirth in another woman (OR 2.4, 95% CI 1.1-5.5)., Conclusion: Live preterm birth, fetal growth restriction, preeclampsia, and abruptio placenta are strongly associated with later stillbirth., Level of Evidence: II.

Self-selection in epidemiological studies may introduce selection bias and influence the validity of study results. To evaluate potential bias due to self-selection in a large prospective pregnancy cohort in Norway, the authors studied differences in prevalence estimates and association measures between study participants and all women giving birth in Norway. Women who agreed to participate in the Norwegian Mother and Child Cohort Study (43.5% of invited; n = 73 579) were compared with all women giving birth in Norway (n = 398 849) using data from the population-based Medical Birth Registry of Norway in 2000-2006. Bias in the prevalence of 23 exposure and outcome variables was measured as the ratio of relative frequencies, whereas bias in exposure-outcome associations of eight relationships was measured as the ratio of odds ratios. Statistically significant relative differences in prevalence estimates between the cohort participants and the total population were found for all variables, except for maternal epilepsy, chronic hypertension and pre-eclampsia. There was a strong under-representation of the youngest women (<25 years), those living alone, mothers with more than two previous births and with previous stillbirths (relative deviation 30-45%). In addition, smokers, women with stillbirths and neonatal death were markedly under-represented in the cohort (relative deviation 22-43%), while multivitamin and folic acid supplement users were over-represented (relative deviation 31-43%). Despite this, no statistically relative differences in association measures were found between participants and the total population regarding the eight exposure-outcome associations. Using data from the Medical Birth Registry of Norway, this study suggests that prevalence estimates of exposures and outcomes, but not estimates of exposure-outcome associations are biased due to self-selection in the Norwegian Mother and Child Cohort Study.

Background/aim: Parents whose first infant had birth defects may worry about a new pregnancy. Our aim was to study pregnancy outcomes among non-malformed second siblings in families where the first birth had a major birth defect., Methods: Data were from the Medical Birth Registry of Norway from 1967 to 2004. Births were linked to their mothers through the unique national identification numbers, providing sibship files with the mother as the observation unit. The study was based on 538,669 singleton first and second full siblings. Families were classified as affected families if the first infant had a major birth defect. Pregnancy outcomes for non-malformed second siblings following affected first births were compared with second siblings in families without malformed infants. Subgroup analyses were done for families where first infants had neural tube defects, cleft lip with or without cleft palate, abdominal wall defects, limb reduction defects, pes equinovarus and congenital dysplasia of the hip., Results: Second siblings in affected families did not differ from those in unaffected families in risk of perinatal death, small for gestational age, preterm birth, placental abruption or preeclampsia. Second siblings following an infant with limb reduction defects had a higher risk of breech presentation than second siblings in unaffected families, also when stratifying on previous siblings in vertex presentation (stratified OR 2.20 [95% C.I. 1.17-4.15])., Conclusion: Parents who proceed to a new pregnancy after a first birth with birth defects may be reassured that, given no recurring defects, there is in general no increased risk of adverse pregnancy outcomes.

Objective: To investigate intergenerational recurrence of breech delivery, with a hypothesis that both women and men delivered in breech presentation contribute to increased risk of breech delivery in their offspring., Design: Population based cohort study for two generations., Setting: Data from the medical birth registry of Norway, based on all births in Norway 1967-2004 (2.2 million births)., Participants: Generational data were provided through linkage by national identification numbers, forming 451,393 mother-offspring units and 295,253 father-offspring units. We included units where both parents and offspring were singletons and offspring were first born, forming 232,704 mother-offspring units and 154,851 father-offspring units for our analyses., Main Outcome Measure: Breech delivery in the second generation., Results: Men and women who themselves were delivered in breech presentation had more than twice the risk of breech delivery in their own first pregnancies compared with men and women who had been cephalic presentations (odds ratios 2.2, 95% confidence interval 1.8 to 2.7, and 2.2, 1.9 to 2.5, for men and women, respectively). The strongest risks of recurrence were found for vaginally delivered offspring and were equally strong for men and women. Increased risk of recurrence of breech delivery in offspring was present only for parents delivered at term., Conclusion: Intergenerational recurrence risk of breech delivery in offspring was equally high when transmitted through fathers and mothers. It seems reasonable to attribute the observed pattern of familial predisposition to term breech delivery to genetic inheritance, predominantly through the fetus.

Objective: To validate Down syndrome registration in the Medical Birth Registry of Norway (MBRN), 2001-2005, and study time trends and geographical differences in Down syndrome prevalence,1967-2005., Design/setting: Population-based cohort study, Norway., Population: 2.3 million pregnancies and births registered in the MBRN, 1967-2005., Methods: We linked data from the MBRN during 2001-2005 with data from Norway's four laboratories of medical genetics. We calculated sensitivity and positive predictive values (PPV) of the MBRN registration overall, and by background variables. Prevalence rates from 1967 to 2005, overall and regional, were presented graphically as smoothed lowess estimates, crude and standardized for maternal age. Time trends were evaluated, adjusting for maternal age by logistic regression., Main Outcome Measures: Sensitivity, PPV, and prevalence rates., Results: Five hundred and seventy-six verified cases of Down syndrome gave a prevalence of 2.0 per 1,000 among 288,213 births and terminations in the MBRN during 2001-2005. Of verified cases, 470 (81.6%) were registered with Down syndrome in the MBRN, while 470 (90.2%) of 521 MBRN-registered cases were verified. Sensitivity was higher in the Northern (93.1%; p=0.005) and Middle (90.6%; p=0.02) region relative the Southern (76.3%), higher for mothers > or =35 years (92.9%) than younger ones (86.1%; p=0.01), and higher for live births (88.8%) relative stillbirths (55.6%; p<0.001). When adjusting for maternal age, there were no significant time trends in prevalence rates from 1967 to 2005. Regional differences over time were found, probably representing reporting differences., Conclusions: Validity of registration in the MBRN was satisfactory during 2001-2005. Increasing prevalence rates over time were explained by increasing maternal age.

Background: To compare first-time parenthood probability and pregnancy outcome between cancer patients and the general population., Methods: Data from a hospital registry on cancer patients aged 15-35 years at diagnosis, including date/type of diagnosis, treatment and date of death, were merged with data from the Cancer Registry and the Medical Birth Registry, providing date of childbirth, IVF, pregnancy outcomes and demographics., Results: The first-time parenthood probability at the age of 35 years was 63% in male patients (n = 463) and 64% in the male general population (n = 367 068). Figures in female patients were 66% (n = 284) compared with 79% in the female general population (n = 349 576) (P = 0.007). A total of 487 male and 251 female cancer patients were childless pre-diagnosis, and 130 male and 104 female cancer patients had one child before diagnosis and at least one birth post-diagnosis. Congenital anomalies were more frequent in first-borns to previously childless male patients [adjusted odds ratio (OR(adj)): 1.5; 95% confidence interval (CI): 1.1-2.3]. The risk of low birth weight and preterm delivery after cancer was increased in infants born to female patients, as was perinatal mortality (OR(adj) 2.3; 95% CI: 1.1-5.0) among post-diagnosis first births., Conclusions: The first-time parenthood probability in 35-year old cancer patients is approximately 60%, which in female patients is significantly reduced compared with the general population. Post-diagnosis pregnancies to female patients are high-risk pregnancies.

Purpose: To evaluate the role of semen cryopreservation (SCP) in the fertility saving management of testicular cancer (TC) patients, treated at the Norwegian Radium Hospital between 1983 and 2002., Patients and Methods: 422 of 1388 newly diagnosed TC patients had SCP All patients were followed up for post-treatment paternity., Results: During the 20 years study period, by 2002 an increasing percentage of patients had pre-treatment SCP, reaching 43% after 1994. Twenty-nine (7%) of the 422 patients with SCP had used their frozen semen for assisted reproductive techniques (ART) at least once to achieve fatherhood. Pregnancies were achieved in 16 of these patients' partners, but two of these pregnancies ended in abortions. 67(17%) of 393 men with SCP fathered at least one child without use of frozen semen. The comparable figures for those without SCP were 205 out of 966(21%). Twenty years after orchiectomy the cumulative incidence of first post-treatment fatherhood was 47% for the 393 patients who had SCP but did not use it for ART, and 34% for the 966 patients without SCP (p=0.12)., Conclusion: If offered, about 50% of the young and middle-aged patients newly diagnosed with TC are interested in pre-treatment SCP. Though our study reveals that a considerable number of TC patients referred to SCP, achieve fatherhood without the use of frozen semen, the psychological impact of pre-treatment cryopreservation is undeniable. Furthermore, for some TC survivors ART with cryopreserved sperm offers the only chance of post-treatment paternity.

Background: Birthweight distributions among second-born infants depend on the birthweights of older siblings, with implications for weight-specific perinatal mortality. We wanted to study whether these relations were explained by socioeconomic levels, and to study time trends in a situation with decreasing perinatal mortality rates., Methods: Births in the Norwegian Medical Birth Registry from 1967 to 1998 were linked to their mothers through their national identification numbers. The study population was 546 688 mothers with at least two singletons weighing >/==" BORDER="0">500 g at birth. Weight-specific perinatal mortality for second-born siblings in families with first-born siblings in either the highest or the lowest birthweight quartile was analysed. Maternal education and cohabitation status were used as measures of socioeconomic level., Results: For all 500-g categories below 3500 g, mortality rates were significantly higher among second-born infants with an older sibling in the highest rather than the lowest weight quartile. This pattern was the same across three educational levels. The exclusion of preterm births did not change the effect pattern. A comparison of perinatal mortality among second siblings in terms of relative birthweight (z-scores) showed a reversal of the relative risks, although these were only significantly different from unity for the smallest infants. Conclusion The crossover in weight-specific perinatal mortality for second siblings by weight of first sibling is largely independent of socioeconomic level, and is not weakened by the decreasing perinatal mortality rates in the population over time. Family data should be taken into consideration when evaluating the risk of adverse pregnancy outcome relating to weight.

Infants with congenital malformations have on average lower birth weight than do infants without malformations. Preterm delivery and low birth weight are known to recur in sibships. The aim of the study was to compare the birth weight of siblings to malformed infants with the birth weight of infants in families without malformed infants. Data were from the Medical Birth Registry in Norway from 1967 to 1998. Births were linked to their mothers through the unique personal identification number, providing sibship files with the mother as the observation unit. The study was based on 551,478 mothers with at least two singleton infants and 209,423 mothers with at least three singletons. The authors grouped the families according to whether and in which birth order an infant had a registered congenital malformation and compared birth weight and gestational age between infants of the same birth order in families with malformations and without. Overall, in families where one or two infants had a congenital malformation, the crude and adjusted mean birth weight of nonmalformed siblings did not differ from that of infants in unaffected families, whereas it was significantly reduced for the malformed infant itself. We conclude that reduced birth weight associated with congenital anomalies is specific to the affected pregnancy.

Our objective was to study birthweight among surviving siblings in families with and without a perinatal loss, and to evaluate whether different causes of death were associated with the results. Data were for 1967-98 from the Norwegian Medical Birth Registry. Births were organised with the mother as the observation unit through the personal identification number, providing sibship files. We analysed 550 930 sibships with at least two singletons, 208 586 sibships with at least three singletons and 45 675 sibships with at least four singleton births. We compared mean birthweight and gestational age between infants in sibships with and without a perinatal loss, total losses and the different causes of death. Surviving siblings in families with a perinatal loss had significantly lower mean birthweights than their counterparts in unaffected families, after adjusting for gestational age, interpregnancy interval, time period and marital status. An exception was found when cause of death was a birth defect, when growth retardation among surviving siblings was not found on average. We conclude that families who have lost an infant because of a birth defect do not appear to have an increased risk of adverse birth outcome associated with growth restriction.

Aim: To investigate whether variations in birth length (crown-heel-length) were associated with perinatal mortality rate independent of birth weight., Material: The study population was singleton live- and stillbirths from 16 weeks of gestation compiled in the Medical Birth Registry of Norway from 1967 to 1997, totaling 1,705,652 births., Method: The total population was analyzed using z-scores for length at birth, birth weight and gestational age. Variation in perinatal mortality by length at birth was studied within birth weight strata (250 g) by logistic regression., Results: Perinatal mortality varied more by birth length than by birth weight or gestational age, especially for values above the population means. Within birth weight strata, the association between perinatal mortality and length was similar in all 250 g birth weight categories above 1,500 grams: mortality was lowest at birth lengths 0-2 cm below average, with mortality rates increasing exponentially in either direction., Conclusion: Within all birth weight strata, and adjusted for gestational age, long infants had the higher risk of perinatal death, suggesting that length at birth may be a valuable predictor when assessing the risk of perinatal mortality.

The authors studied the extent to which preterm birth and perinatal mortality are dependent on the gestational ages of previous births within sibships. The study was based on data collected by the Medical Birth Registry of Norway from 1967 to 1995. Newborns were linked to their mothers through Norway's unique personal identification number, yielding 429,554 pairs of mothers and first and second singleton newborns with gestational ages of 22-46 weeks, based on menstrual dates. Siblings' gestational ages were significantly correlated (r = 0.26). The risk of having a preterm second birth was nearly 10 times higher among mothers whose firstborn child had been delivered before 32 weeks' gestation than among mothers whose first child had been born at 40 weeks. However, perinatal mortality in preterm second births was significantly higher among mothers whose first infant had been born at term, compared with mothers whose firstborn child was delivered at 32-37 weeks. Since perinatal mortality among preterm infants is dependent on the gestational age in the mother's previous birth, a common threshold of 37 weeks' gestation for defining preterm birth as a risk factor for perinatal death may not be appropriate for all births to all mothers.

Objective: To study possible indicators for subclinical eating disorders among teenage girls., Design: A descriptive cross-sectional study based on two anonymous self-report questionnaires., Setting: Girls aged 15 to 19 years in secondary high school in Bergen, Norway., Subjects: 100 girls, mean age 16.6 years, were included. One girl fulfilled DSM-III-R criteria for bulimia nervosa, and was therefore excluded from analysis. Ten girls fulfilled criteria for subclinical eating disorders., Main Outcome Measures: The Eating Disorder Examination Questionnaire and a 48-item questionnaire designed for the study were used. Attitudes towards own body size/weight, food habits, and somatic symptoms were studied., Results: Girls with subclinical eating disorders experienced their own body as fatter and were more unhappy with their weight than girls without eating problems. They more often skipped breakfast or lunch, reported more dyspeptic problems and regurgitation, and had a larger weight fluctuation than girls without eating problems., Conclusion: Questions about main meals may serve as neutral opening questions for the general practitioner when case finding in eating disorders. Obviously unrealistic feelings about body size/weight indicate the need to enquire more closely about symptoms of eating disorders.