Forbes: During pregnancy, the body naturally produces more melatonin than it normally does.
Healthline explains that when you’re pregnant, your ovaries and placenta produce higher levels of melatonin and use it throughout your pregnancy and delivery. The publication reports that your melatonin levels rise at 24 weeks and then again at 32 weeks. So, taking a melatonin supplement on top of this while pregnant will mean your melatonin levels are much more elevated than pre-pregnancy.
While your natural levels of melatonin are higher during pregnancy, there are very few studies that look at how supplementing these levels could have adverse effects or benefits. MGH Centre for Women’s Mental Health writes, “although melatonin is indeed natural and is normally produced by the body, the amount delivered by various over-the-counter preparations typically exceeds the quantities normally produced by the body. As is the case with most supplements, we know very little about the impact these high levels of hormones may have on the developing fetus. Thus, we typically advise women with sleep problems to use medications with a better characterized reproductive safety profile.”