Pregnancy

Melatonin should be considered to be contraindicated in pregnancy at this time.(1) In pregnant women, endogenous melatonin crosses the placenta and enters the fetal circulation, and appears to be responsible for setting circadian rhythm influences in utero. Melatonin receptors in the fetus are widespread in both central and peripheral tissues from the third week of fetal development. The administration of exogenous melatonin could potentially disrupt circadian entrainment and other pineal gland influences.(21) Thus, fetal exposure to exogenous melatonin use in the mother may be of concern. Effects in non-clinical animal studies of melatonin were observed only at exposures considered sufficiently in excess of the maximum human exposure indicating little relevance to clinical use; however, the data are limited.(2) In animal studies, ramelteon, a melatonin analog, produced evidence of developmental toxicity, including teratogenic effects, in rats at doses much greater than the recommended human dose.(19) The potential effects of melatonin on the duration of labor and/or obstetric delivery, for either the mother or the fetus, have not been studied. Melatonin has no established use in labor and delivery.