Differential effect of advanced maternal age on prenatal diagnosis of trisomies 13, 18 and 21

Nondisjunction associated with advanced maternal age, a well-established fa ctor in the etiology of autosomal trisomy, should equally affect all chromo somes. in this study we evaluate the association of advanced maternal age w ith the occurrence of potentially viable autosomal trisomies (13, 18 and 21 ), 275 aneuploid pregnancies were ascertained prenatally and were grouped a ccording to chromosome anomaly diagnosed. Mean maternal age was significant ly younger (p = 0.009) in pregnancies affected by trisomy 13 than in pregna ncies with trisomy 21. An intermediate mean maternal age was observed in pr egnancies affected by trisomy 18. Our study shows a trend of the more sever e, but potentially viable, autosomal trisomies to be diagnosed at younger m aternal age. This may substantiate the 'relaxed selection hypothesis' propo sed to explain the association of aneuploid conceptions with advanced mater nal age.