Chromosomal abnormality rates at amniocentesis and in live-born infants

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Abstract
Regression-smoothed maternal age-specific rates of 6 different categories of cytogenetic abnormalities in recent large-scale prenatal cytogenetic studies were multiplied by independently derived fetal selection coefficients-factors that adjust for the excess likelihood of spontaneous loss of cytogenetically abnormal fetuses-to obtain estimated maternal age-specific rates of these categories of cytogenetic abnormalities in live-born infants. The derived rates apply to women whose only risk factor is advanced maternal age. The categories analyzed were 47,+21 (Down''s syndrome), 47,+18 (Edwards'' syndrome), 47,+13 (Patau''s syndrome), 47,XXY (Klinefelter''s symptom), 47,XXX and the group of other clinically significant abnormalities considered collectively. The rate of all clinically significant abnormalities considered together derived in this study was about 5/1000 at age 35 yr, 15/1000 at age 40 yr and 50/1000 at age 45 yr.