Maternal age and preterm births in infants conceived by in vitro fertilization in the United States

In natural conception advanced maternal age (≥ 35 years) is associated with an increased risk of preterm birth. However, few studies have specifically examined this association in births resulting from in vitro fertilization (IVF). We conducted a retrospective cohort study of 97,288 singleton and 40,961 twin pregnancies resulting from fresh non-donor IVF cycles using 2006-2010 data from the Society for Assisted Reproductive Technology Clinic Online Reporting System. Rates of very early preterm (<28), early preterm (<32), and preterm birth (<37 completed weeks) decreased with increasing maternal age in both singleton and twin births (P-_Trend <0.01). In both singletons and twins, with women aged 30-34 years as the referent, women aged ≤ 30 years were at increased risk of all types of preterm births. The increased risk of preterm births among younger women was even more significant in twins than in singletons. The adjusted odd ratios (95 % confidence intervals) of very early preterm twin birth, early preterm twin birth, and preterm twin birth in women aged <25 were 1.7(1.2-2.2), 1.3 (1.1-1.6), and 1.5 (1.3-1.8) (all P <0.01). However, women aged ≥ 35 years were not at increased risk of all types of preterm births in both singleton and twin births. The authors conclude that, in contrast to natural conception, advanced maternal age is not associated with increased risk of preterm births in infants conceived by IVF. Women who seek IVF treatments before 30 years old are at higher risk of all types of preterm births.