OBJECTIVE To investigate the influence of maternal and cord serum and amniotic fluid growth hormone (GH) and insulin and other neonatal and maternal factors on birthweight. METHODS A total of 160 pregnant women at 38-42 weeks' gestation were studied. All infants were categorized as small for gestational age (SGA) (n = 50), large for gestational age (LGA) (n = 50) or average for gestational age (AGA) (n = 60). GH and insulin levels were measured in maternal and cord serum and amniotic fluid at birth. RESULTS GH levels in maternal and cord serum and amniotic fluid showed no differences among the three weight groups (P > 0.05). The cord insulin level was significantly lower in SGA (P < 0.01). The insulin level in venous cord blood correlated with birth and placental weights and neonatal height, whereas maternal serum and amniotic fluid insulin levels, and maternal and cord serum and amniotic fluid GH levels did not show any correlation with birthweight. The cord GH level at birth was correlated with GH levels after 4 postnatal weeks in the SGA group (P < 0.01). In addition, birthweight showed a correlation with prepartum maternal weight, maternal weight gain, maternal height, neonatal length and placental weight in all three weight groups. CONCLUSIONS Cord GH, maternal serum and amniotic fluid GH and insulin levels did not correlate with birthweight in all three weight groups. The lack of correlation for GH levels in maternal and cord serum and amniotic fluid suggests that these compartments may be non-communicating separate units.