Fig 3. Association between weight variation before pregnancy and birth weight mediated by gestational weight gain for women with pre-pregnancy BMI < 25 kg/m².

Effect size β (95% CI). All models were adjusted for maternal education level, maternal age, smoking before and during pregnancy, place of birth, parity, health insurance coverage, activity status, and pre-pregnancy BMI. Birth weight z-score according to the French Audipog reference [26]. *Sobel test of indirect effect p < 0.001.