Background: Fetal macrosomia, defined as birth weight equal or over 4000 g, is a major concern for both neonatal and maternal health. A rapid increasing trend in fetal macrosomia is observed in different regions of China. We aimed to examine the association between fetal macrosomia and risk of childhood obesity in Western China.

Methods: All macrosomic live singletons (≥ 4000 g), and a random sample of singletons with normal birth weight (2500–3999 g) born in four districts of Chengdu, Western China, in 2011 were included in the cohort study. Maternal demographics, obstetric factors, labor and delivery summary at baseline were extracted from the Chengdu Maternal and Child Health Management System. Anthropometric measurements before 3 years and infant feeding information at around 6 months were also collected. Childhood obesity under 3 years was primarily defined as a weight-for-length/height z score ≥ 1.645 using the WHO growth reference. Secondary definitions were based on weight-for-age and body mass index (BMI)-for-age over the same cut-offs.

Results: A total of 1767 infants were included in the analyses, of whom 714 were macrosomic. After controlling for maternal age, parity, gestational age and anemia at the fi rst antenatal visit, pre-pregnancy BMI, gestational weight gain, gestational age at birth, baby age and sex, and breastfeeding practices at 6 months, the risk of childhood obesity defined according to weight-for-length/height among macrosomic babies was 1.90 (95% confidence interval 1.04–3.49) times that of babies with normal birth weight. The risk of childhood obesity for macrosomic babies was 3.74 (1.96–7.14) and 1.64 (0.89–3.00) times higher based on weight-for-age and BMI-for-age, respectively.