The association between maternal weight gain and spontaneous preterm birth in twin pregnancies.

Objective: To estimate the association between maternal weight gain and SPTB in twin pregnancies.

Methods: A case-control study of patients with twin pregnancies and a normal prepregnancy BMI (18.5-24.9 kg/m(2)) in one maternal-fetal medicine practice from 2005 to 2013. We reviewed maternal weight in six time periods: prepregnancy, 12-15 6/7 weeks, 16-19 6/7 weeks, 20-23 6/7 weeks, 24-27 6/7 weeks and 28-31 6/7 weeks. We compared maternal weight gain patterns across pregnancy between patients who did and did not have SPTB <32 weeks. Student's t-test and chi-square were used for analysis.

Results: In total, 382 patients were included, 29 (7.6%) of whom had SPTB <32 weeks. The baseline height, weight and BMI did not differ between the groups, nor did maternal age, IVF status, race or chorionicity. Patients with SPTB <32 weeks had significantly less weight gain as early as 15 6/7 weeks (2.9 ± 4.6 versus 7.3 ± 6.6 lb, p < 0.001), and this continued until 31 6/7 weeks (25.3 ± 8.7 versus 30.8 ± 10.9 lb, p = 0.037).

Conclusions: In twin pregnancies with a normal prepregnancy BMI, there is a significant association between SPTB <32 weeks and lower maternal weight gain, particularly prior to 16 weeks. Future studies are needed to test if prepregnancy or early nutritional interventions in twin pregnancies can reduce the risk of preterm birth and improve neonatal outcomes in this high-risk population.