Pre-pregnancy BMI-specific optimal gestational weight gain for women in Japan

Background: The Institute of Medicine (IOM) guidelines are the most widely used guidelines on gestational weight gain; however, accumulation of evidence that body composition in Asians differs from other races has brought concern regarding whether their direct application is appropriate. We aimed to study to what extent optimal gestational weight gain among women in Japan differs by pre-pregnancy body mass index (BMI) and to compare estimated optimal gestational weight gain to current Japanese and Institute of Medicine (IOM) recommendations. Methods: We retrospectively studied 104,070 singleton pregnancies among nulliparous women in 2005-2011 using the Japanese national perinatal network database. In five pre-pregnancy BMI sub-groups (17.0-18.4, 18.5-19.9, 20-22.9, 23-24.9, and 25-27.4 kg/m²), we estimated the association of the rate of gestational weight gain with pregnancy outcomes (fetal growth, preterm delivery, and delivery complications) using multivariate regression. Results: Weight gain rate associated with the lowest risk of adverse outcomes decreased with increasing BMI (12.2 kg, 10.9 kg, 9.9 kg, 7.7 kg, and 4.3 kg/40 weeks) for the five BMI categories as described above, respectively. Current Japanese guidelines were lower than optimal gains, with the lowest risk of adverse outcomes for women with BMI below 18.5 kg/m², and current IOM recommendations were higher than optimal gains for women with BMI over 23 kg/m². Conclusion: Optimal weight gain during pregnancy varies largely by pre-pregnancy BMI, and defining those with BMI over 23 kg/m² as overweight, as proposed by the World Health Organization, may be useful when applying current IOM recommendations to Japanese guidelines.