Human chorionic gonadotropin (hCG) is a pregnancy-specific hormone that regulates placental development. hCG concentrations vary widely throughout gestation and differ based on fetal sex. Abnormal hCG concentrations are associated with adverse pregnancy outcomes including fetal growth restriction. We studied the association of hCG concentrations with fetal growth and birth weight. In addition, we investigated effect modification by gestational age of hCG measurement and fetal sex. Total serum hCG (median 14.4 weeks, 95 % range 10.1–26.2), estimated fetal weight (measured by ultrasound during 18–25th weeks and >25th weeks) and birth weight were measured in 7987 mother–child pairs from the Generation R cohort and used to establish fetal growth. Small for gestational age (SGA) was defined as a standardized birth weight lower than the 10th percentile of the study population. There was a non-linear association of hCG with birth weight (P = 0.009). However, only low hCG concentrations me
