* This table includes only chromosomal abnormalities that can be detected by standard chromosomal testing. Risks of having a baby with submicroscopic chromosomal abnormalities (which can be detected only by special testing) are not included.

Data based on information in Hook EB: Rates of chromosome abnormalities at different maternal ages. Obstetrics and Gynecology 58:282-285, 1981; Hook EB, Cross PK, Schreinemachers DM: Chromosomal abnormality rates at amniocentesis and in live-born infants. Journal of the American Medical Association 249 (15):2034-2038, 1983; and Savva GM, Walker K, Morris JK. The maternal age-specific live birth prevalence of trisomies13 and 18 compared to trisomy 21 (Down syndrome). Prenatal Diagnosis 30:57–64, 2010.