Cytogenetic evidence for enhanced selective miscarriage of trisomy 21 pregnancies with advancing maternal age.

The effect of advancing maternal age on the risk of death of fetuses with certain chromosome abnormalities has been tested by comparing their frequency at the time of chorionic villus sampling (CVS) with that at amniocentesis. The frequency of chromosome abnormalities among women whose sole risk factor for a chromosome abnormality was advanced maternal age (> or = 35 years old) was determined in a pooled group of 15,147 CVS cases, of whom > 1/3 were from the initial 7,500 CVS cases at the University of California, San Francisco, and compared with a pooled group of 74,851 amniocentesis cases collected from the literature. The frequency of trisomy 21 not only increased with advancing maternal age as expected, but the slope of the increase was about 25% greater in the CVS group than in the amniocentesis group (P = 0.08 for the difference in slopes by a logistic statistical model and P = 0.04 by a normit model). Similar patterns were seen for trisomies 18 and 13, but the P values for the differences in slopes were much higher. These results suggest that the miscarriage rate of trisomy 21 during the gestational interval studied is selectively greater with advancing maternal age. The basis for the enhanced selective loss of trisomy 21 with maternal age may be a reduced ability of the ageing "maternal compartment" to compensate for abnormal conceptuses.