Multifetal pregnancy in older women and perinatal outcomes.

OBJECTIVE: To examine multifetal pregnancy in older women and perinatal outcomes.
DESIGN: A cross-sectional study.
SETTING: A nationwide vital registry. PATIENT(S): A national population-based database that links the live birth, fetal, and infant death certificates reported of multiple gestations in the United States from 1995 to 1997. It includes 155,777 twin and 5,630 triplet pregnancies. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Very preterm birth (<33 weeks), very low birthweight (<1,500 g), and perinatal and infant deaths. RESULT(S): Compared with those with singleton pregnancies, women with multifetal gestation tended to be older, non-Hispanic white, better educated, married, and nulliparous and to have earlier and more frequent prenatal care. Pregnancies conceived by assisted reproductive technology accounted for an increasing number of multiple gestations in older women. In women with lower socioeconomic status, older age was associated with higher risks of poor perinatal outcomes in twin pregnancy (relative risks ranging from 1.0 to 1.9 with a dose-response pattern). However, in women with higher socioeconomic status, older women did not have a higher risk of poor perinatal outcomes than younger women. CONCLUSION(S): The effect of older maternal age on perinatal outcomes in multifetal pregnancies may have been altered by assisted reproductive technology, frequent prenatal surveillance, and advanced neonatal care.