Background. We wanted to determine the relationship between a number of maternal characteristics and various fetal and neonatal anthropometric measurements determined by ultrasound and at birth. Methods. A total of 1205 term singleton maternal-infant pairs were studied. Various ultrasound measurements obtained at 18, 24, 30 and 36 weeks' gestation and neonatal anthropometric measurements obtained at birth were studied in relationship to various maternal characteristics using univariate and multivariate techniques. Results. Black race, female sex, cigarette smoking, drug use, having a previous low birthweight infant, maternal hypertension and being short or thin or failing to gain weight each resulted in a birthweight decrease of 100 to 300 g. The effect of each of these characteristics on each ultrasound measurement, the timing of the effect, and its ultimate effect on neonatal anthropometric measurements are described. Conclusion. The data presented in this paper provide a more complete understanding of the relationship between maternal characteristics, infant sex, and various fetal ultrasound and neonatal measurements.