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Women who become pregnant soon after the birth of a child may have a higher risk of premature delivery. Researchers in Denmark examined the interpregnancy intervals of 10,187 women who had given birth to two children. Pregnancies which began within eight months of a previous birth were associated with preterm delivery, but not with low birth weight. A short interval between pregnancies may alter hormonal balance or prevent recovery of nutritional reserves.

Objective--To confirm or refute reports that vasectomy may increase the risk of cancers of the testis and prostate. Design--Computerised record linkage study of cohort of men with vasectomy and comparison [...]

Objective The aim of this study was to compare reproduction patterns among Danish women born with isolated oral clefts versus the Danish background population.Design and Setting A nationwide population-based historic cohort study based on three registers: The Danish Facial Cleft Register, The Danish Civil Registration System, and the Fertility of Women and Couples Dataset.Participants Through linkages of the registers, the number of children and the exact age at childbirth of all Danish women born with an oral cleft from 1950 through 1988 (N = 1931) were obtained. These data were compared with similar data for the entire Danish female background population (N = 1,184,390).Results and Conclusions This study suggests that childlessness is higher among women born with an oral cleft (55%) than among women in the Danish background population (44%). Excluding women without children, women born with oral cleft had an average of 1.98 children per woman. This did not differ significantly from the background population (2.02 children/woman). Furthermore, the present study found that Danish women born with oral clefts on average were older (27.3 years of age) than the background population (24.7 years of age) when they had their first child (difference = 2.6 years, confidence interval = 2.41 to 2.80).Conclusion Danish women born with an oral cleft more often are childless or have their first child later, but if they have children, they tend to have as many children as other Danish women. Social, psychological, and biological reasons might be responsible for the reduced fertility.

Some malformations are clearly associated with older maternal age, but the effect of older age of the father is less certain. The aim of this study is to determine the degree to which maternal age and paternal age independently influence the risk of having a child with oral clefts.

Objective The aim of this project was to assess whether any changes in the birth prevalence of cleft lip with/without cleft palate (CL[P]) occurred in Denmark during the period 1988 through 2001. In this period an official recommendation of a supplementation of folic acid to pregnant women was introduced; furthermore, smoking among pregnant women decreased considerably.Design and Settings There are few places in which ecological studies of oral clefts are possible. Denmark provides a particularly good setting for this kind of study because of a high ascertainment and a centralized registration of subjects with cleft over the last 65 years.Participants Cleft occurrence in Denmark from 1936 to 1987 has previously been reported. Here we extend the study to include all live-born children with oral clefts born in Denmark in 1988 through 2001. Among a total of 992,727 live births, 1332 children with CL(P) were born during this period.Results and Conclusions The birth prevalence of CL(P) in Denmark has previously been found to be constant in the period 1962 through 1987, with a frequency of 1.4 to 1.5 per 1000 live births. This study showed a similar occurrence in 1988 through 2001 (birth prevalence = 1.44 per 1000 live births, 95% confidence interval = 1.37 to 1.52). The introduction of folic acid and the decrease in smoking prevalence among pregnant women do not seem to have reduced the birth prevalence. This may be due to noncompliance with the folic acid recommendation and/or only a weak causal association between folic acid and smoking and occurrence of CL(P).

During past decades, we have witnessed a remarkable decline in fertility rates (number of births per 1000 women of reproductive age) in the industrialized world. It seems beyond doubt that the enormous social changes of our societies play the major role in this decline, but can it be attributed to changing social structures alone or is a reduced fecundity in the population also a factor? To address this we have focused on trends in teenage pregnancies (which to a large extent are unplanned). During the period in question fertility rates among 15-19 year old Danish women have been falling and the decline in fertility rate is not counterbalanced by an increase in the rate of induced abortion. When seen together with recent results from Denmark, which have shown that more than 30% of 19 year old men from the general population now have sperm counts in the subfertile range, we argue that this fall may not be attributable to social factors, changes in conception practices or diminished sexual activity alone. It seems reasonable also to consider widespread poor semen quality among men as a potential contributing factor to low fertility rates among teenagers. Due to the concern caused by the low sperm count among younger Danish men, the Danish Ministries of Health and Environment have launched a surveillance programme which includes an annual examination of the semen quality in 600 young Danes from the general population. We propose that researchers in other countries with low and falling fertility rates among young women should consider the possibility that semen quality of their younger male cohorts may also have deteriorated.

It has been suggested in the literature that twinning rates are reduced by psychosocial stress associated with urban life. No support for this hypothesis was found in a study based upon the 5762 twins and 280158 singletons that were born in Denmark in the period 1978 to 1982.

Using data from seven malformation monitoring systems around the world, the feasibility of monitoring fresh dominant mutations using skeletal dysplasias was explored. Based on a total of over 9.5 million births, 1500 infants with skeletal dysplasias were identified (16 per 100000). In spite of efforts to get exact diagnoses, an average of 21% were unspecified. Comparisons of rates of specific diagnoses in different programmes suggested that classification differed. By analysing maternal age distribution, estimates were made of the proportion of fresh mutations in different subgroups: conditions regarded as dominant (achondroplasia, thanatophoric dysplasia, spondyloepiphyseal dysplasia) were estimated to consist of 58% fresh mutations-some of the remaining cases were inherited, others were probably misclassified. Among conditions regarded as recessive, only 5% were estimated to be truly dominant mutations. In the total group of skeletal dysplasias, 21% were estimated to be fresh dominant mutations and if osteogenesis imperfecta were excluded, the figure was 31%. By power analyses it was shown that equal monitoring power may be obtained by a programme covering about 45 000 births per year with intensive diagnosis of each individual case of skeletal dysplasia and a programme some three times greater where no specific diagnoses are obtained. An increasing trend in the occurrence of skeletal dysplasias was seen but probably explained by changing ascertainment. An impact of antenatal diagnosis resulting in a decrease in occurrence was also apparent in some programmes.