Gestational bodyweight gain among underweight Japanese women related to small-for-gestational-age birth

Aim: The prevalence of underweight women, who have an increased risk for small-for-gestational-age (SGA) birth, is increasing in Japan. We examined the associations of pre-pregnancy body mass index and gestational weight gain (GWG) with SGA birth among Japanese women. Material and Methods: We conducted a prospective cohort study of 1391 women who delivered full-term singleton babies. SGA was defined as below the 10th percentile of birthweight at each gestational age, baby sex, and parity. We calculated the 5th percentile of birthweight in the same way for another threshold for SGA. According to pre-pregnancy body mass index, we divided the participants into three groups: underweight (