Macrosomia, defined as a birth weight of ≥4000 g, is associated with a high risk of birth injury. Fetal growth is highly correlated with maternal conditions, and several maternal factors are associated with neonatal birth size. The current study aimed to assess maternal factors related to fetal macrosomia in a Taiwanese population. The medical records of pregnant mothers and their newborns were retrospectively reviewed. All singleton pregnancies delivered at and after 37 weeks of gestation were included in the analysis. Maternal and neonatal conditions were evaluated according to different birth weights. A total of 4262 infants were enrolled in our study. The mean birth weight was 3156 ± 383 g, including 77 (1.8%) cases with birth weight ≥4000 g, and 154 (3.6%) infants with birth weight <2500 g. The mean maternal body weight before delivery was 67.6 ± 10.0 kg. The mean 6-month gestational weight gain (6mGWG) was 12.3 ± 4.2 kg, and the mean maternal body mass index (BMI) was 26.2 ± 3.6 kg/m 2 . The maternal weight, height, and 6mGWG, gestational age, and placental weight were significantly positively correlated with neonatal birth weight. The odds ratios of macrosomia were 3.1 in neonates born to mothers with a 6mGWG of ≥15 kg, 6.3 in those born to mothers with gestational diabetes mellitus, and 4.1 in those born to mothers with a BMI of ≥30 kg/m 2 . Newborn macrosomia was associated with adverse events in pregnant mothers and newborn infants. Gestational diabetes mellitus, 6mGWG, and maternal BMI are significantly correlated with neonatal macrosomia in full-term singleton births. Further, neonatal macrosomia is an important cause of maternal and neonatal morbidity. Hence, pregnant women should undergo maternal counseling for weight management before and during pregnancy, and the appropriate delivery method should be identified to prevent perinatal adverse events.