Association between women's weight gain during their infancy and being overweight or underweight in adulthood: a retrospective cohort study.

This study aimed to explore the associations between weight gain during infancy with pre-pregnant body mass index (BMI) later in life, focusing on risks of being overweight or underweight. A retrospective cohort study was conducted using data from women (n = 1082) who visited the National Center for Child Health and Development between 2017 and 2021. The participants provided their Maternal and Child Health Handbook, which included records of their own birthweight and weight gain from birth to 1, 3, and 6 months. The infant weight gain was divided into quintiles. Multivariable logistic regression was used to assess the association of weight gain during infancy with pre-pregnant underweight (BMI < 18.5) and overweight (BMI ≥ 25) later in life, adjusting for potential confounders. The current study found that the largest weight gain category (5230-7700 g) by 6 months was associated with a decreased risk of "pre-pregnant underweight," compared to the third weight gain category (4355-4730 g) by 6 months (OR, 0.40; 95% CI, 0.22-0.73). In contrast, no significant association was observed between weight gain category in infancy and being overweight in adulthood. In conclusion, greater weight gain during the first 6 months of life was associated with a reduced risk of "adult underweight," without increasing the risk of being overweight.