Contemporary risks of maternal morbidity and adverse outcomes with increasing maternal age and plurality

To evaluate the risks of pregnancy complications and adverse outcomes associated with increasing maternal age and higher plurality.

Population-based, historic cohort study.

US birth certificates and infant death certificates.

Live births of > or =20 weeks gestation between 1995-2000: 22,991,306 singleton, 316,696 twin, and 12,193 triplet pregnancies.

None.

Pregnancy-associated hypertension, incompetent cervix, tocolysis, premature rupture of membranes, excessive bleeding at delivery, delivery <29 weeks, and infant death.

Compared to singletons, the risks for all adverse outcomes among multiple pregnancies were significantly elevated, and were highest for tocolysis, delivery <29 weeks, and infant mortality. Within pluralities, increasing maternal age was associated with significantly higher risks of pregnancy-associated hypertension, excessive bleeding, and incompetent cervix, but for twin and triplet pregnancies, significantly lower risks for tocolysis (ages > or =40, singleton adjusted odds ratio [AOR] 0.97, twin AOR 0.67, triplet AOR 0.72), delivery <29 weeks (ages > or =40, singleton AOR 1.55, twin AOR 0.72, triplet AOR 0.52), and infant mortality (ages > or =40, singleton AOR 1.34, twin AOR 0.71, triplet AOR 0.42).

Older maternal age and higher plurality are each associated with increasing risks for many pregnancy complications, but with significantly lower risks of tocolysis, early preterm birth, and infant mortality.