The association between gestational weight gain and perinatal outcomes among underweight women with twin pregnancy in Japan.

Objective: To clarify the association between gestational weight gain (GWG) and pregnancy outcomes in underweight women with twin pregnancies in Japan.

Methods: This retrospective study derived data from the Japan Society of Obstetrics and Gynecology perinatal database between 2007 and 2015. We included 5049 underweight (pre-pregnancy body mass index [BMI] <18.5 kg/m2 ) and 20 812 (BMI ≥18.5 and <25 kg/m2 ) normal-weight, twin-pregnant women. Weekly GWG was stratified into 10 categories. Logistic regression was used to assess the effects of GWG on pregnancy. The primary outcomes evaluated were small-for-gestational age (SGA), preterm birth, preeclampsia, and cesarean delivery.

Results: In underweight group, high GWG was associated with significant risk reductions in both twins being SGA, at least one twin being SGA, very preterm birth, and extreme preterm birth, while a risk increase was observed in preeclampsia. Compared to women with GWG of 0.25-0.30 kg/week, the risk of preeclampsia was significantly higher in women with GWG >0.35 kg/week. No association was observed between GWG and cesarean delivery. These associations were similar in the normal-weight group.

Conclusions: Underweight women with twin pregnancies showed an inverse association between GWG and SGA or preterm birth. The risk of preeclampsia was higher in women who gained >0.35 kg/week.