Effect of maternal height and weight on risk for preterm singleton and twin births resulting from IVF in the United States, 2008-2010

Objective: To analyze the effects of preconception maternal height and weight on the risk of preterm singleton and twin births resulting from in vitro fertilization (IVF).

Study design: We performed a retrospective cohort analysis of the incidence of very early preterm birth (VEPTB), early preterm birth (EPTB), and preterm birth (PTB), before 28, 32, and 37 completed weeks, respectively, in 60,232 singleton and 24,111 twin live births using 2008-2010 live birth outcome data from the Society for Reproductive Technology Clinic Outcome Reporting System.

Result: Maternal obesity is associated with significantly increased risk of VEPTB, EPTB, and PTB in pregnancies conceived by IVF. For morbidly obese women (body mass index ≥35) with singletons, rates of VEPTB, EPTB, and PTB were 1.7%, 3.6%, and 16.4%, with adjusted risk ratios (aRRs) and 95% confidence levels (CIs) of 2.6 (1.8-3.6), 2.2 (1.8-2.6), and 1.5 (1.4-1.7) using corresponding rates for normal body mass index (95% CI, 18.6-24.9) as referent. For morbidly obese women with twins, rate of VEPTB and EPTB were 6.5% and 12.5%, with aRRs and 95% CIs of 2.4 (1.8-3.0) and 1.5 (1.3-1.8). For singletons, the rate of PTB for short stature women (<150 cm) was 14.2%, as compared with 11.8% in those women with height ranging between 160-167 cm (referent), with aRRs and 95% CIs of 1.2 (1.0-1.4).

Conclusion: Preconception maternal obesity and short stature are associated with significantly increased risk of VEPTB and early preterm singleton and twin births in pregnancies resulting from IVF.