Melatonin is already deeply involved in pregnancy, whether or not you take a supplement. Your body ramps up melatonin production as pregnancy progresses, with levels climbing significantly above non-pregnant baselines and peaking in the third trimester. The placenta itself manufactures the hormone and uses it to manage oxidative stress, support fetal development, and relay day-night timing information to the baby. But the question most pregnant people actually have is about supplemental melatonin, the kind sold in pill or gummy form for sleep, and there the picture is far less settled.
Your Body Already Makes More Melatonin When You Are Pregnant
Melatonin is not just a sleep hormone. During pregnancy, it takes on a second life as an antioxidant and signaling molecule, and your body responds by producing considerably more of it. A study measuring serum melatonin across pregnancy found that levels were significantly higher in pregnant women than in non-pregnant women and increased steadily throughout gestation, with the highest concentrations appearing in the third trimester.1PubMed Central. Maternal Serum Melatonin Increases During Pregnancy and Falls Immediately After Delivery Implicating the Placenta as a Major Source of Melatonin Within 24 hours of delivery, levels dropped sharply, suggesting that the placenta is a major contributor to the elevated melatonin seen during pregnancy.
The placenta does not just pass along melatonin from the pineal gland. Placental tissue contains the enzymes needed to synthesize melatonin on its own, and these enzymes are active from early pregnancy through term.2PubMed. Placental melatonin system is present throughout pregnancy and regulates villous trophoblast differentiation The same tissue also expresses melatonin receptors in multiple cell types, including the trophoblast cells that form the placental barrier and the endothelial cells lining fetal capillaries.3PubMed. Human placental trophoblasts synthesize melatonin and express its receptors First-trimester placental tissue already carries these receptors and enzymes, so the system is operational well before melatonin levels peak later in pregnancy.4PubMed. Melatonin as a local regulator of human placental function
What Melatonin Does for the Placenta and the Fetus
Inside the placenta, melatonin acts primarily as an antioxidant and anti-inflammatory agent. Pregnancy naturally generates oxidative stress as the placenta metabolizes oxygen at high rates, and melatonin helps keep that stress in check by scavenging free radicals and maintaining placental tissue integrity.5PubMed Central. Melatonin: the placental antioxidant and anti-inflammatory In animal studies of nutritionally compromised pregnancies, melatonin treatment improved placental efficiency, boosted the expression of protective antioxidant enzymes, and restored birth weight to normal levels.6PubMed. Melatonin improves placental efficiency and birth weight and increases the placental expression of antioxidant enzymes in undernourished pregnancy
The fetus cannot make its own melatonin. Its pineal gland does not fully develop until after birth, so until that point it depends entirely on the mother’s supply, which crosses the placenta freely.7PubMed Central. Role of melatonin in embryo fetal development8PubMed. Melatonin and pregnancy in the human This maternal melatonin does more than protect against oxidative damage. It also provides the fetus with photoperiodic information, essentially a daily light-dark signal that helps set the stage for the baby’s own circadian rhythms after birth.
Animal Evidence for Brain Protection
Some of the most striking research on melatonin during pregnancy involves its potential to protect the developing fetal brain from oxygen deprivation. In late-gestation fetal sheep subjected to acute low-oxygen events, maternal melatonin administration reduced cell death in the brain, prevented breakdown of the blood-brain barrier, and lowered markers of inflammation and oxidative damage.9PubMed. Mechanisms of melatonin-induced protection in the brain of late gestation fetal sheep in response to hypoxia Similar work in preterm fetal sheep showed that melatonin brought cell death and brain inflammation back to control levels across multiple brain regions after oxygen deprivation.10Frontiers in Cellular Neuroscience. The Beneficial Effects of Melatonin Administration Following Hypoxia-Ischemia in Preterm Fetal Sheep
A Cochrane review looking specifically at melatonin for fetal brain protection during pregnancy confirmed that animal studies support a neuroprotective role but found no completed randomized controlled trials in humans to draw from at the time of review.11PubMed Central. Melatonin for women in pregnancy for neuroprotection of the fetus That gap is important: the animal findings are consistent and encouraging, but translating them to human clinical practice remains an open question. Preliminary data suggests melatonin may also have direct growth-promoting effects on developing brain tissue, beyond just preventing damage.12PubMed Central. Melatonin as a Therapy for Preterm Brain Injury: What Is the Evidence?
Is It Safe to Take Melatonin Supplements During Pregnancy?
This is where most readers’ real concern lies, and the honest answer is that the evidence is thin. A scoping review of human studies on melatonin use during pregnancy and breastfeeding found no randomized controlled trials that examined melatonin specifically for treating sleep disorders in pregnant or nursing women. Trials that did use exogenous melatonin during pregnancy for other conditions did not report major safety concerns or adverse events.13Brazilian Journal of Psychiatry. Melatonin use during pregnancy and lactation: A scoping review of human studies But “no major safety concerns reported in a handful of small trials” is a long way from “proven safe.” The absence of harm in limited studies is not proof that harm does not exist.
In rats given high oral doses of melatonin during pregnancy, researchers found no effects on fetal survival, fetal weight, or rates of birth defects, even at doses hundreds of times larger per kilogram of body weight than what humans typically take. Maternal side effects at very high doses included reduced appetite and mild sedation, but the fetal development side showed no problems at any dose tested.14Toxicological Sciences. Maternal and developmental toxicity evaluation of melatonin administered orally to pregnant Sprague-Dawley rats Animal toxicology is reassuring but does not settle the question for humans.
One phase I trial gave melatonin to 20 women diagnosed with early-onset preeclampsia. The treatment appeared safe for both mothers and fetuses. Compared to matched controls receiving similar care, the women on melatonin stayed pregnant an average of six additional days before delivery and needed fewer increases in blood pressure medication.15PubMed. Melatonin improves endothelial function in vitro and prolongs pregnancy in women with early-onset preeclampsia That trial was designed to test safety and feasibility, not to establish efficacy, and 20 participants is far too small to detect rare adverse effects. Still, it is one of the few direct glimpses we have of supplemental melatonin in human pregnancy, and it was encouraging.
Most professional guidelines do not recommend for or against melatonin during pregnancy because the evidence base simply is not large enough to issue firm guidance. If you are struggling with sleep and considering a melatonin supplement, this is a conversation for your prenatal care provider, who can weigh your individual situation against the current uncertainty.
Preeclampsia and Fetal Growth Restriction
Two pregnancy complications where melatonin has drawn serious research interest are preeclampsia and fetal growth restriction, both of which involve oxidative stress and poor placental blood flow.
In preeclampsia, the blood vessels supplying the placenta do not develop properly, leading to high blood pressure and organ damage. Laboratory and animal work suggests melatonin counteracts the endothelial damage seen in preeclampsia by reducing oxidative stress and dampening inflammation. Recent research found that melatonin’s protective effects on endothelial cells in preeclampsia models depended on its receptor MT1, and that blocking that receptor diminished the benefits.16PubMed. CD34 in preeclampsia: The role of endothelial cell pyroptosis and regulation by melatonin via melatonin membrane receptor 1 The human preeclampsia trial described above, while small, offered early clinical evidence pointing in the same direction.17PubMed. Melatonin improves endothelial function in vitro and prolongs pregnancy in women with early-onset preeclampsia
Fetal growth restriction, where the baby grows more slowly than expected, is often linked to compromised blood flow through the placenta. In sheep, melatonin supplementation increased umbilical artery blood flow and rescued measures of fetal head and organ size that had been stunted by nutrient restriction.18PubMed. Melatonin supplementation alters uteroplacental hemodynamics and fetal development in an ovine model of intrauterine growth restriction In mice, melatonin improved gut barrier and placental integrity under heat stress, leading to better nutrient transport and increased fetal weight.19PubMed Central. Effect of melatonin as a therapeutic strategy against intrauterine growth restriction: a mini-review of current state Both lines of evidence are from animals, and it is worth emphasizing that growth restriction in humans has many causes; whether melatonin supplementation would help in any specific clinical scenario remains tested only in very early-stage research.
Preterm Labor
Preterm birth is driven in part by uterine inflammation, and melatonin’s anti-inflammatory properties have made it a target of investigation here too. In a mouse model where bacterial toxins were used to trigger premature labor, melatonin treatment prevented preterm birth in half of cases. All pups born to melatonin-treated mothers were alive at birth, with normal body weight, compared to worse outcomes in untreated animals.20PubMed. Melatonin prevents experimental preterm labor and increases offspring survival Melatonin lowered levels of prostaglandins, nitric oxide, and inflammatory signaling molecules in the uterus, all of which drive premature contractions. A separate mouse study confirmed that maternally administered melatonin modulated the immune response to inflammation and decreased both preterm birth and brain injury in surviving pups.21PubMed. Administration of melatonin for prevention of preterm birth and fetal brain injury associated with premature birth in a mouse model
Again, these are animal studies, and there is a substantial gap between preventing inflammation-triggered preterm birth in a mouse and doing the same in a human pregnancy where preterm labor has many different triggers. But the consistency of the animal findings across multiple labs and models has kept melatonin on the radar as a potential future intervention.
Why Night Shifts and Screen Time May Matter More Than You Think
If the body’s own melatonin production matters this much during pregnancy, then anything that disrupts it deserves attention. A case-series study of pregnant night-shift workers found that their melatonin production was suppressed during night shifts, and they had lower overall nighttime melatonin compared to day-working pregnant women. Their newborns also showed lower Apgar scores and more breastfeeding difficulty, suggesting worse initial adaptation to life outside the womb.22PubMed Central. Melatonin profiles during the third trimester of pregnancy and health status in the offspring among day and night workers: A case series
A broader review linked artificial light at night to a wide range of adverse pregnancy outcomes, including reduced fertility, sleep disturbances, preterm birth, metabolic changes, gestational diabetes, altered gut bacteria, mood symptoms, excessive weight gain, fetal growth changes, and even congenital heart defects.23PubMed Central. Melatonin and Artificial Light: Effects on Maternal and Fetal Health During Pregnancy Animal studies in the review showed that disrupting melatonin through light exposure caused measurable harm to offspring development, while melatonin supplementation reversed some of that harm. The practical takeaway is that protecting your natural melatonin production through basic sleep hygiene, dimming lights in the evening, minimizing bright screens before bed, keeping your bedroom dark, may be at least as meaningful as debating whether to take a supplement.
Melatonin and Longer-Term Programming
Researchers have also explored whether melatonin during pregnancy influences how fetal genes are switched on or off in ways that persist after birth. In pregnancies complicated by conditions like gestational diabetes, growth restriction, or maternal undernutrition, oxidative stress can alter gene expression through epigenetic changes, modifications that do not change the DNA sequence itself but can change how genes behave. Melatonin’s ability to neutralize oxidative stress during pregnancy may help prevent some of these damaging modifications from taking hold.24PubMed Central. Roles of melatonin in fetal programming in compromised pregnancies This area of research is still early-stage and mostly theoretical, but it raises the intriguing possibility that melatonin’s effects during pregnancy might extend well beyond the delivery room.
After Birth: Melatonin in Breast Milk
Newborns do not produce meaningful amounts of their own melatonin for the first few months. A recognizable circadian rhythm in infant melatonin typically does not appear until around the third month of life. During that gap, breast milk serves as the primary natural source of melatonin for the baby.25PubMed Central. Melatonin in Human Breast Milk and Its Potential Role in Circadian Entrainment: A Nod towards Chrononutrition? Melatonin concentrations in breast milk follow the mother’s own circadian cycle, peaking after midnight and dropping during the day. This is thought to help synchronize the infant’s developing sleep-wake rhythm with the mother’s. Breastfed infants have been observed to sleep longer than formula-fed infants, and the melatonin content of breast milk is one plausible explanation.
The melatonin content of breast milk also varies with gestational age and the stage of lactation, suggesting the system is tuned to match the infant’s changing needs over time. Some researchers have called for more attention to what they term “chrononutrition,” the idea that when a baby feeds matters for circadian development, not just what and how much they consume. For mothers who pump milk, this raises a practical question: should expressed milk from nighttime sessions be labeled and given at night? Some researchers think so, though formal guidelines on this do not yet exist.
Melatonin Before Pregnancy: IVF and Egg Quality
Melatonin’s antioxidant properties have also attracted interest in the fertility space, particularly for women undergoing IVF. Melatonin is naturally present in follicular fluid, the liquid surrounding eggs inside ovarian follicles, where it helps protect developing eggs from oxidative damage.26PubMed Central. Importance of Melatonin in Assisted Reproductive Technology and Ovarian Aging
In one trial, women taking melatonin before an IVF cycle had a higher proportion of mature eggs and more high-quality embryos, though pregnancy rates trended higher without reaching statistical significance.27PubMed. The efficacy of melatonin administration on oocyte quality More striking results came from a study of women aged 38 and older, where melatonin supplementation during IVF significantly increased clinical pregnancy rates, ongoing pregnancy rates, and live birth rates compared to controls.28PubMed Central. Melatonin supplementation attenuates cuproptosis and ferroptosis in aging cumulus and granulosa cells: potential for improving IVF outcomes in advanced maternal age The researchers found that melatonin protected the cells surrounding the egg from forms of oxidative cell death that become more common with age. These findings are promising for the pre-pregnancy period, though it is important not to conflate them with evidence about taking melatonin during pregnancy itself. The timing, context, and goals are different.
The broader pattern across all of this research is consistent: melatonin is a molecule the reproductive system takes seriously, from egg maturation through placentation, fetal development, and newborn nutrition. The science of supplementing it during pregnancy simply has not caught up to the biology yet. Large, well-designed human trials are still needed, and until those exist, the gap between “biologically important” and “proven safe and effective as a supplement” remains wide.