Previous reproductive history in mothers presenting with spontaneous abortions

Information on the previous reproductive history of 3467 mothers presenting with a spontaneous abortion is compared with that of a control series presenting with a livebirth. In 1384 abortions the chromosome constitution of the fetal products was determined. The mothers who had delivered a chromosomally normal abortion more often had a history of previous repeated abortions, while those of chromosomally abnormal abortions tended to have fewer repeated abortions but an excess of previous viable children with Down's syndrome. Data are also presented on 23 mothers with two spontaneous abortions of known karyotype; these, together with similar data obtained elsewhere, made it possible to estimate an overall rate of recurrence of chromosome defects in conceptions of the same parents, and the probability that affected fetuses will survive to a viable stage in pregnancy. The clinical and genetic implications of the findings are briefly discussed.