Circulating leptin in women: a longitudinal study in the menstrual cycle and during pregnancy

OBJECTIVE To investigate whether leptin is linked to reproduction, circulating levels were measured longitudinally throughout spontaneous menstrual cycles and during pregnancy in normal women.

DESIGN Longitudinal blood samples were collected from normal volunteers, either during regular menstrual cycles or during successful singleton pregnancies.

PATIENTS Six healthy, regularly cycling, women volunteers (31.5+3.0 years old, BMI=21.6+0.5) were recruited for serial venous blood sampling throughout one complete menstrual cycle. In addition, five healthy, women (31.8 +/- 1.2 years old, pre-pregnant BMI=30.0+/-3.1) provided serial venous blood samples throughout one complete singleton pregnancy.

MEASUREMENTS Circulating venous oestradiol, progesterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), leptin and (pregnant group only) human chorionic gonadotrophin (hCG).

RESULTS In spontaneously cycling women, changes in circulating leptin levels were associated with menstrual phase (P<0.001) and correlated with progesterone levels (P<0.05). Peak leptin concentrations were recorded during the luteal phase (P<0.01), coincident with maximal progesterone levels (P<0.05). Leptin concentrations were elevated throughout gestation (P<0.05), and especially during the second trimester (P<0.05). Post-partum, circulating leptin levels fell sharply to below pre-pregnant values. Leptin correlated with oestradiol (P<0.05) and human chorionic gonadotrophin (hCG, (P<0.01) levels during pregnancy. First trimester (P<0.05) and postpartum (P<0.05) oestradiol concentrations and post-partum hCG levels exhibited the greatest correlation with circulating leptin.

CONCLUSIONS We conclude that the relationship between body mass index and circulating leptin varies during the course of spontaneous cycles in women, the best correlation occurring during the luteal phase when progesterone and leptin concentrations are highest. This, together with the correlation between circulating oestradiol, hCG and leptin levels during pregnancy, strongly suggests a dynamic relationship between leptin and reproductive events in women.