Background <p>Evidence indicates that excessive gestational weight gain and maternal pre-pregnancy BMI contribute to unhealthy childhood BMI and the global obesity epidemic. This study examined their effects on early childhood obesity.</p> Methods <p>This retrospective cohort study included 230 mother-infant pairs. Children born between 2019 and 2021 who were aged 2 years were included. Maternal data (height, weight, BMI, and GWG) and children’s anthropometric data (height, weight, and BMI z-scores) at 0, 1, 3, 6, 12, 18, and 24 months of age were collected from medical records.</p> Results <p>This study included 230 mother-infant pairs. The median pre-pregnancy maternal BMI was 25.51 (17.72–46.47) kg/m², and the mean weight gain during pregnancy was 10.8 ± 4.8 kg. Before pregnancy, 3.5% of mothers were underweight, 32% were overweight, and 21% were obese. During pregnancy, 35% of mothers gained insufficient weight, and 28% gained excessive weight.</p> <p>A significant relationship was found between maternal BMI and the BMI z-score determined at the third-month follow-up of the child (p=0.03). </p> <p>A significant relationship was found between the mother's weight gain during pregnancy and the child's BMI z-score at twelve months and twenty-four months (p=0.033 and p=0.047, respectively).</p> Conclusion <p>Excessive gestational weight gain corresponded to higher BMI z-scores at ages 1 and 2 years, and a higher maternal pre-pregnancy BMI was related to the infant BMI z-score at 3 months. These findings indicate that gestational weight gain is a modifiable factor with implications for the risk of early childhood obesity</p> Clinical trial number <p>Not applicable.</p>