Oxytocin concentrations increased during pregnancy and during medication with low-dose oral contraceptives (o.c.). Postprandial somatostatin concentrations were lower during medication with o.c. Insulin concentrations were elevated during pregnancy with the same tendency during medication with o.c. Gastrin levels were unaffected during the peripartal period and during medication with o.c. Women who were breastfeeders at 3 months after delivery had higher concentrations of oxytocin and lower somatostatin concentrations post-prandially during pregnancy and fasting at 3 months after delivery compared with non-breastfeeders at 3 months after delivery. Metabolic and behavioral implications are discussed.