Impact of prepregnant body mass index and maternal weight gain on the risk of pregnancy complications in Japanese women

Background. To analyze the association of pregnancy complications with prepregnant body mass index and weight gain during pregnancy in Japanese women. Methods. A retrospective cohort study was conducted with 21,718 Japanese women with a singleton pregnancy. Pregnant women were grouped by prepregnant body mass index and evaluated for association with pregnancy complications using multivariate logistic regression analysis. The women in each body mass index group were then divided into groups by weight gain during pregnancy using intervals of 0.05 kg/week to analyze the relationship between the weight gain and pregnancy complications by multivariate logistic regression association analysis. Results. In both nulliparous and parous women, the least pregnancy complications were found among women with medium prepregnant body mass indexes (18–23.9). Significant risks of pregnancy complications were associated with low (<18) and high (≥24) prepregnant body mass indexes, particularly high prepregnant body mass indexes. In nulliparous women, the optimal weight gain was 0.25–0.4 kg/week for low (<18) prepregnant body mass index, 0.20–0.30 kg/week for medium (18–23.9) prepregnant body mass index, and ≥0.05 kg/week for high (≥24) prepregnant body mass index. In parous women, the corresponding values were ≥0.20, 0.20–0.30, and 0.05–0.30 kg/week. Conclusions. Japanese women with prepregnant body mass indexes from 18 to 23.9 are least associated with pregnancy complications, although there is a broad range of prepregnant body mass indexes associated with few pregnancy complications. Optimal weight gain is roughly inversely related to prepregnant body mass index.