Aneuploidy in twin gestations: When is maternal age advanced?

Objective: To determine the maternal age at which twin gestations have a risk of fetal aneuploidy comparable to that of singleton pregnancies at maternal age 35, accounting for variation in dizygotic twinning rates by maternal age and race. Methods: Known aneuploidy risks and rates of dizygotic twinning by maternal age and race were used to calculate the risk of fetal aneuploidy at term and in the second trimester by maternal age and race in twin gestations, using previously published calculations. Results: The risk of at least one aneuploid twin at term is 1/193 at maternal age 31 for both white and African-American women, which is comparable to the risk of 1/192 for an aneuploid singleton term pregnancy at maternal age 35. The risk of at least one aneuploid twin at amniocentesis at maternal age 31 is 1/190 for white and 1/187 for African-American women, which is slightly lower than the rate in singletons of 1/135. Conclusion: Invasive prenatal diagnosis for detection of fetal aneuploidy should be offered to all women with twin gestations at age 31, regardless of race. Copyright (C) 1997 by The American College of Obstetricians and Gynecologists.