The effect of prepregnancy body mass index on singleton cesarean delivery among term nulliparous women in Japanese population

Purpose Overweight or obesity is a known risk factor for cesarean delivery although there is minimal data among Japanese women. The aim of the study was to examine the effect of prepregnancy body mass index (BMI) on singleton cesarean delivery among term nulliparous women using a national sample from the Human Milk Survey. Methods Data from the Human Milk Survey between 1998 and 2008 were used for the secondary analysis. Women were categorized as underweight (BMI < 18.5 kg/m(2)), normal weight (18.5 a parts per thousand currency sign BMI < 25.0), or overweight (BMI a parts per thousand yen 25.0) based on their prepregnancy BMI. The association between maternal prepregnancy BMI and cesarean delivery was assessed using logistic regression models. Results A total of 915 women were included in the analysis. The proportion of cesarean section was 10.1%. Overall, 17.1% of the women were underweight while 6.0% were overweight. After adjusting for maternal age, smoking status, pregnancy complications, and infant birthweight, overweight women were 2.7 times more likely to have a cesarean delivery compared to normal weight women (adjusted odds ratio [adjusted OR] = 2.7, 95% confidence interval [CI] = 1.4-5.4), and underweight women were half as likely to have a cesarean delivery compared to normal weight women (adjusted OR = 0.5, 95% CI = 0.2-1.1). Conclusions Being overweight before pregnancy more than doubled the risk of cesarean delivery independent of age, smoking, pregnancy complications, and infant birthweight among term nulliparous women. Overweight Japanese women should be advised to achieve normal prepregnancy BMI in their preconception period to prevent cesarean delivery.