Effect of maternal height and weight on risk of preterm birth in singleton and twin births resulting from in vitro fertilization: a retrospective cohort study using the Society for Assisted Reproductive Technology Clinic Outcome Reporting System

ObjectiveTo examine the effect of height, weight, and body mass index (BMI) on the risk of preterm birth of singleton and twin pregnancies conceived by vitro fertilization (IVF).DesignRetrospective cohort study using 2006–2008 data from the Society for Reproductive Technology Clinic Outcome Reporting System (SART CORS).SettingSART-associated assisted reproductive technology programs.Patient(s)56,556 singleton and 23,804 twin live births resulting from fresh nondonor IVF cycles.Intervention(s)None.Main Outcome Measure(s)Rates of very early preterm (VEPTB; <28 weeks), very preterm (VPTB; <32 weeks), and preterm birth (<37 weeks) births.Result(s)In both singleton and twin births, increased maternal height was associated with a decreased risk of preterm birth. Maternal overweight and obesity were associated with significantly increased risk of VEPTB and VPTB in twin pregnancies. For very obese women (BMI > 35 kg/m2) twins were associated with a threefold increased risk of VEPTB (6.1% vs. 2.0%) and a twofold increased risk of VPTB (11.5% vs. 5.9%) compared with women of normal weight (BMI 18.4–24.9 kg/m2).Conclusion(s)Obesity and short stature significantly increase the risk of VEPTB and VPTB in twins conceived by IVF.