Association of pre-pregnancy body mass index and gestational weight gain with continued breastfeeding until 6 months postpartum in Japanese women: the Japan Environment and Children's Study.

Abstract

Background: The relationship of pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) with continued breastfeeding (BF) in Japanese women remains unclear. To evaluate different maternal pre-pregnancy BMI and GWG categories according to the initial BMI, we conducted an analysis of continued BF until 6 months postpartum in a large Japanese cohort.

Methods: This study used data from the Japan Environment and Children's Study, which included approximately 100,000 pregnant women. Pre-pregnancy BMI (kg/m²) was categorized as underweight (BMI < 18.5), normal weight (BMI 18.5-24.9), and overweight (BMI 25.0-29.9). GWG was categorized as insufficient, optimal, and excessive based on the 2021 criteria from the Japanese Society of Obstetrics and Gynecology. Continued BF for the first 6 months postpartum was categorized into 3 patterns: exclusive BF (EBF), non-EBF type-I (6 months of BF with formula), and non-EBF type-II (< 6 months of BF). Logistic regression analysis was conducted to evaluate the association of pre-pregnancy BMI and GWG with continued BF. Normal BMI and optimal GWG and EBF were used as reference values while controlling for covariates.

Results: Of 82,129 women with singleton pregnancies, BMI was categorized as underweight in 16.6%, normal weight in 75.3%, and overweight in 8.1%. The rate of EBF in these groups was 37.1% for underweight, 37.2% for normal weight, and 26.8% for overweight. In underweight women, both insufficient and excessive GWG were associated with higher rates of non-EBF type-II. In normal-weight women, insufficient and excessive GWG were associated with higher rates of non-EBF type-II. Overweight women showed higher rates of non-EBF type-I and type-II, irrespective of GWG.

Conclusions: Our results indicate that the effects of GWG on continued BF were associated with pre-pregnancy BMI. Adequate GWG should be recommended to underweight and normal-weight women to promote BF. Efforts toward the prevention of overweight prior to pregnancy should be encouraged to enhance BF.