Origin of chromosomal abnormalities: evidence for delayed fertilization in meiotic nondisjunction.

This study ascertained 35 aneuploid patients, of which 34 had trisomy 21 and one had trisomy 18. Their parents were matched by age at the conception with parents of 35 euploid patients with congenital defects. Interviews with the couples focused on exposures and activities at the time of the conception. No parents had infectious hepatitis preceding the conception, and one study mother and four comparison parents reported drug ingestion. Eight parents in the study group and two in the comparison reported radiation exposure. One family in each group had a history of thyroid disorder. The groups differed mainly in their sexual histories; circumstances favoring the possibility of delayed fertilization (contraceptive failure, infrequency of intercourse, or premarital conception) existed in 22 of the study group but in only seven of the comparison group.