Gestational weight gain according to number of fetuses in Japanese women.

Aim: It is unknown whether weekly maternal weight gain differs between Japanese women with singleton, twin, and triplet pregnancies.

Methods: Gestational weight gain defined as net weight gain during pregnancy was analyzed in 135,036 pregnant Japanese women, including 128,838 with singletons, 5573 with twins, and 132 with triplets, who gave birth at ≥22 weeks of gestation between 2007 and 2009. Weekly weight gain was defined as follows: gestational weight gain÷[gestational week (GW) at Delivery-2].

Results: Length of gestation (weeks, mean±SD) decreased significantly (38.2±2.6, 35.3±3.0, and 32.7±2.8) with increasing number of fetuses, while overall gestational weight gain (kg) was significantly smaller in women with singletons than in those with either twins or triplets (9.6±4.4 vs. 10.9±4.8 or 10.9±5.2, respectively). Thus, weekly maternal weight gain (kg/week) increased significantly with increasing number of fetuses (0.26±0.12, 0.33±0.13, and 0.35±0.16). Among women with delivery at or after GW 34, difference in gestational weight gain (kg) was prominent between the three groups (9.8±4.4, 11.4±4.7, and 13.0±5.1 for singleton, twin, and triplet pregnancies, respectively, P<0.001 between any two groups).

Conclusions: Weekly maternal weight gain increases with increasing number of fetuses. Our figures may be useful for advising Japanese women with multifetal pregnancies regarding gestational weight gain.