Sex chromatin and chromosome abnormalities among 10,412 liveborn babies.

Among 10,412 livebom infants surveyed in a large maternity hospital in a 2-year period, there were 13 cases (0.13%) of discrepancy between sex phenotype and sex chromatin (0.15% among male infants and 0.10% among female infants). There were 22 cases of trisomy-21 (incidence 0.21%), 3 cases of trisomy-18, and 1 case of trisomy-13-15. 9 cases presented multiple congenital abnormalities but the karyotype was normal. Only the incidence of cases with Down's syndrome is higher than that reported in the literature. Maternal and paternal age, seasonal clustering, infectious diseases before or at the beginning of pregnancy, and x-ray exposure of parents, showed no correlation with Down's syndrome. Among the cases of Down's syndrome there was a significantly higher maternal and paternal mean age and a maternal history of infectious hepatitis was more frequent.