Epidemiology of Down syndrome in 118,265 consecutive births.

The epidemiology of Down syndrome (DS) was studied in the area which is covered by our registry of congenital malformations. For each of the 139 new DS cases which were ascertained during the period 1979 to 1987 more than 50 factors were studied and compared to those from control infants. The prevalence of DS was 1.17%; 3.6% of the DS cases were stillbirths and 14.4% were induced abortions. Karyotypes were obtained in 137 cases of which all but 7 were 47, + 21, 4 were mosaics (2.8%), and 5 had translocations (3.6%). Interchromosomal effect was a question in 3 cases. The most common types of associated malformations were cardiac anomalies (44.6%) and intestinal atresia. We did not observe seasonality or time/space clusters in spite of the Chernobyl nuclear accident. No paternal age effect was demonstrated. In our material the first-born infants were at lower risk of DS than the later born. Five percent of the mothers of DS had 2 previous spontaneous abortions (controls 2.8%). At birth, the DS infants measured less and their head circumference was lower than in control infants. Weight of placenta was also lower than in control infants. In our material there were 7.9% of consanguineous marriages (P = .010). The pregnancies of the DS children were often complicated by threatened abortions; 6.4% of the mothers of the DS children were diabetic (P = .069). For all other factors studied no statistically significant difference with respect to controls could be demonstrated.