Parental consanguinity as a cause of increased incidence of birth defects in a study of 131,760 consecutive births.

The risk for birth defects in the offspring of first cousin parents is substantially higher than in the offspring of non-consanguineous parents. As a general decline in the frequency of consanguineous marriages was observed in this century, one wonders whether consanguinity is still a factor in the appearance of birth defects in developed countries. Based on our registry of congenital anomalies, we think that the answer to this question is "yes." In the population studied in Northeastern France, consanguineous matings were known in 1.08% of the cases with congenital anomalies, vs. 0.28% in controls (P < 0.001). The frequency of the malformations recorded paralleled the degree of consanguinity: out of 38 malformed children, 24 were seen in first cousin matings (10.5 times more frequent than in offspring of nonconsanguineous couples), 8 in second cousin marriages, and 6 in more distantly consanguineous matings. Consanguineous mothers were more often pregnant than nonconsanguineous mothers (P < 0.01) and they had more stillbirths than nonconsanguineous mothers. These results must be taken into account when counseling consanguineous couples.