ABSTRACT Introduction: Maternal weight directly influences fetal growth and birth weight, with implications for perinatal health. Objective: To estimate the variation in birth weight according to the adequacy of gestational weight gain in Peruvian pregnant women. Methods: Analytical, retrospective case-control study conducted between 2022 and 2024 at Hospital María Auxiliadora (Lima, Peru). A total of 196 newborns were included: cases with fetal macrosomia (≥4 000 g) and controls with adequate weight. Multiple pregnancies, preterm, post-term, or incomplete records were excluded. The dependent variable was the difference in grams between neonatal weight and 4 000 g. The main independent variable was the difference in maternal kilograms relative to the gestational weight gain recommended by the Institute of Medicine (IOM), adjusted for pregestational body mass index. Multiple linear reg...