Changes of serum melatonin level and its relationship to feto-placental unit during pregnancy

Serum melatonin concentrations were studied in normal pregnant women and in women with several types of pathologic pregnancies, e.g., twins, preeclamp sia or intrauterine growth retardation (IUGR). Blood samples were collected from the material antecubital vein at 14:00 hr (daytime) and 02:00 hr (nig httime) during pregnancy, and also from the umbilical vein and artery immed iately after delivery. Serum melatonin concentrations were measured by radi oimmunoassay. Daytime serum melatonin levels in normal (single fetus, singl eton) pregnancies were low. While the levels showed an increasing tendency toward the end of pregnancy, no statistically significant changes occurred. On the other hand, the nighttime serum melatonin levels increased after 24 weeks of gestation, with significantly (P < 0.01) high levels after 32 wee ks; these values decreased to non-pregnant levels on the 2nd day of puerper ium. Nighttime serum melatonin levels were significantly (P < 0.05) higher in twin pregnancies after 28 weeks of gestation than in singleton pregnanci es, whereas the patients with severe preeclampsia showed significantly (P < 0.05) lower serum melatonin levels than the mild preeclampsia or the norma l pregnant women after 32 weeks of gestation. Melatonin concentrations in u mbilical vessels showed a higher tendency in neonates who were born during at night compared with the other neonates; moreover, those in the umbilical artery were generally higher than those in the umbilical vein. The present results indicate that in humans, the maternal serum melatonin levels show a diurnal rhythm, which increases until the end of pregnancy, reflecting so me pathologic states of the feto-placental unit. Fetuses may produce melato nin with a circadian rhythm.