Association of parental consanguinity with decreased birth weight and increased rate of early death and congenital malformations.

Data on parental consanguinity have been recorded for all births in Norway since 1967. Pregnancy outcome for offspring of 848 women mated to their first cousins were compared with offspring of 1,696 control women. The stillbirth rate was 23.6 per thousand for cases and 13.4 for controls. The neonatal death rate was 34.9 per thousand for cases and 14.3 for controls. The recurrence risk for sibs for early death was 9.4% for cases and 4.2% for controls. The mean offspring birth weight was significantly lower (3377 g vs. 3491 g), and the variance in birth weight was slightly larger for cases than controls. The percentage of children with malformations detected shortly after birth was 4.6% for cases and 2.2% for controls. The differences may be attributed to the increased homozygosity in offspring of first cousins. The results have relevance for genetic counselling to consanguineous couples, as well as for the understanding of the etiology of adverse pregnancy outcome and for elucidating the causes of variation in birth weight.