Maternal age and birth rank in the aetiology of mongolism.

Abstract

The association beween the incidence of mongolism and maternal age and birth rank was examined by comparing a series of 217 mongoloid infants born in 1942-52 in Birmingham England with a control group of 1156 infants representative of all births in the city during this period. The incidence of mongolism clearly increased with maternal age from a low of 0.31/1000 in the 15-19 and 20-24 year maternal age group to a high of 9.99/1000 in the 45-49 year age group. The incidence of mongolism also increased with birth rank (0.77/1000 at birth rank 1 0.67/1000 at birth rank 2 0.98/1000 at birth rank 3 1.32/1000 at birth rank 4 and 2.07/1000 at birth ranks 5 and above). Further analysis indicated that the association with maternal age is almost independent of birth rank and that association with birth rank is largely eliminated when the influence of maternal age is removed. There is however an excess of mongoloid infants in the 1st birth rank at all maternal ages except 40 years and above. Analysis of a series identified at birth which was the procedure in this study is considered desirable because it avoids the error introduced by the high early mortality of mongoloids and the marked increase in infant mortality from infection with birth order.