Maternal Weight Gain and Pregnancy Outcomes in Twin Gestations.

Abstract Background Data on the optimal gestational weight gain (GWG) in twin pregnancies are limited. As a result, the Institute of Medicine (IOM) currently provides only provisional recommendations on GWG in this population. Objective To identify the optimal range of GWG in twin pregnancies and to estimate the association between inappropriate GWG and adverse pregnancy outcomes. Methods This was a retrospective cohort study of all women with twin pregnancies that were followed in a single, tertiary center between 2000-2014. We used two approaches to identify the optimal range of GWG: a statistical approach (the interquartile range of GWG in low-risk pregnancies with normal outcomes) and an outcome-based approach (by identifying thresholds of GWG below- or above-which the rate of adverse outcomes increases). The primary outcome was preterm birth. Associations of GWG below or above normal range with the study outcomes were estimated using logistic regression analysis and were expressed as adjusted odds ratio (aOR) with 95%-confidence intervals (95%-CI). These associations were stratified by pre-pregnancy BMI group. Results A total of 1,274 women with twin pregnancies met the study criteria: 43 were classified as underweight, 777 were normal weight, 278 were overweight, and 176 were obese. Our estimates of the optimal GWG range were similar to those recommended by the IOM except for the obese category, where our optimal GWG range at 37 weeks (9.3-16.3 kg) was lower than in the provisional IOM recommendations (11.3-19.1 kg). Nearly half of our cohort experienced inappropriate GWG: 30% (n=381) gained weight below and 17% (n=216) gained weight above current IOM recommendations. In the normal weight group, GWG below recommendations was associated with an increased risk of preterm birth and birthweight Conclusions These findings identify GWG as a potentially modifiable risk factor for preterm birth and other pregnancy complications in twin gestations. Further prospective studies are needed to determine whether interventions aimed at optimizing GWG can improve the outcomes of these high-risk pregnancies.