To evaluate the association between gestational weight gain in twin pregnancies and small-for-gestational-age (SGA) and large-for-gestational-age (LGA) birth, preterm birth before 32 weeks of gestation, cesarean delivery, and infant death within each prepregnancy body mass index (BMI) category.
Data in this population-based study came from Pennsylvania-linked infant birth and death records (2003–2013). We studied 54,836 twins born alive before 39 weeks of gestation. Total pregnancy weight gain (kg) was converted to gestational age-standardized z scores. Multivariable modified Poisson regression models stratified by prepregnancy BMI were used to estimate associations between z scores and outcomes. A probabilistic bias analysis, informed by an internal validation study, evaluated the effect of BMI and weight gain misclassification.
Gestational weight gain z score was negatively associated with SGA and positively associated with LGA and cesarean delivery in all BMI groups. The relation between weight gain and preterm birth was U-shaped in nonobese women. An increased risk of infant death was observed for very low weight gain among normal-weight women and for high weight gain among women without obesity. Most excess risks of these outcomes were observed at weight gains at 37 weeks of gestation that are equivalent to less than 14 kg or more than 27 kg in underweight or normal-weight women, less than 11 kg or more than 28 kg in overweight women, and less than 6.4 kg or more than 26 kg in women with obesity. The bias analysis supported the validity of the conventional analysis.
Very low or very high weight gains were associated with the adverse outcomes we studied. If the associations we observed are even partially reflective of causality, targeted modification of pregnancy weight gain in women carrying twins might improve pregnancy outcomes.
Most of the excess risk of poor birth outcomes in twin pregnancies occurs at very high or very low gestational weight gains relative to moderate gains.
Department of Epidemiology, Graduate School of Public Health, the Department of Obstetrics, Gynecology, and Reproductive Sciences, School of Medicine, and the School of Nursing, University of Pittsburgh, and Magee-Women's Research Institute, Pittsburgh, Pennsylvania; the Division of Epidemiology, School of Public Health, University of California, Berkeley, Berkeley, California; the Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, Georgia; the School of Public Health, Oregon Health & Science University-Portland State University, Portland, Oregon; and the Department of Obstetrics & Gynecology, University of British Columbia, Vancouver, British Columbia, Canada.
Corresponding author: Lisa M. Bodnar, PhD, RD, Department of Epidemiology, University of Pittsburgh, Pittsburgh, PA; email: email@example.com.
Supported by NIH grants R21 HD067851 and R01 NR014245. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Financial Disclosure Cara L. Eckhardt disclosed receiving funds paid to her institution from University of Pittsburgh. The other authors did not report any potential conflicts of interest.
Each author has confirmed compliance with the journal's requirements for authorship.
Peer reviews and author correspondence are available at http://links.lww.com/AOG/B577.