Leptin regulates energy homeostasis and immune and metabolic functions. Highly elevated leptin concentrations during pregnancy may be associated with aberrations in maternal metabolism and long-term health consequences both in women and children. The objective of the present study was to evaluate whether dietary counselling, probiotic supplementation, maternal characteristics or dietary intake during pregnancy has an impact on serum leptin concentrations in women, cord blood or in children. A total of 256 pregnant women were randomised to a control group (n 85) or to receive dietary counselling with probiotics (n 85) or placebo (n 86). Dietary counselling aimed at affecting the type of fat used and to increase the amount of fibre in the women's diet. Women's dietary intake and serum leptin concentrations were analysed at the first and third trimesters of pregnancy and at 1 month postpartum. Furthermore, leptin concentrations were measured from the cord blood and from children's serum at 1 and 6 months of age. Weight status and dietary composition were the key determinants of leptin concentrations. Specifically, high dietary fibre and low SFA intakes were related to low serum leptin concentrations in women. Female sex and birth weight were associated with higher infant leptin, whereas cord blood leptin was additionally affected by maternal leptin concentration and protein intake. Probiotics or dietary counselling did not affect leptin concentrations. Weight control to recommended levels and modification of diet towards higher fibre and lower SFA intakes during pregnancy may through leptin concentrations provide health benefits to both women and children.