Melatonin and Artificial Light: Effects on Maternal and Fetal Health During Pregnancy.

INTRODUCTION: The placenta produces melatonin during pregnancy, a hormone essential for circadian regulation and maternal-fetal metabolic, hormonal, and immunological modulation. Throughout pregnancy, melatonin production increases progressively, being synthesized by both the pineal gland and the placenta. Since exposure to artificial light at night (ALAN) reduces pineal melatonin secretion, it is hypothesized that light pollution may negatively impact women's health, maternal health, and fetal development due to the inhibition of both pineal and placental synthesis. MATERIAL AND METHODS: This study aimed to analyze the role of melatonin during pregnancy and the effects of exposure to ALAN on maternal-fetal health. The following search terms ("blue light" OR "ALAN" OR "melatonin") AND ("pregnancy") were applied to Title/Abstract, with the following filters: (i) clinical trials, randomized trials, cohort studies, case-control studies, and case reports; (ii) publications between 2015 and 2025; (iii) studies involving human subjects and nonhuman animal models; (iv) female population; (v) languages: English, Portuguese, or Spanish. Information from the selected articles was extracted and organized into tables, separately for studies in humans and animals (mice and rabbits). RESULTS: Exposure to ALAN reduces melatonin production and is associated with adverse maternal-fetal outcomes, including reduced fertility, sleep disturbances, preterm birth, metabolic alterations, gestational diabetes, hypothyroidism, altered gut microbiota, mood symptoms, excessive gestational weight gain, fetal growth changes, and congenital heart defects. Animal studies demonstrate causal effects of melatonin disruption, including impaired offspring development, inflammation, altered metabolic and hormonal rhythms, and pregnancy complications, whereas melatonin supplementation shows protective effects. These findings highlight the maternal circadian-melatonin axis as a potential target for preventive strategies. Although evidence is insufficient to recommend melatonin supplementation, antenatal counseling may include circadian hygiene measures, such as reducing evening light and screen exposure, maintaining regular sleep schedules, and optimizing nighttime darkness. Light-based interventions, including biodynamic lighting and blue-light-blocking glasses, remain promising but require further clinical validation. CONCLUSION: It is concluded that melatonin plays a central role in regulating pregnancy and that exposure to ALAN poses a risk to maternal-fetal health. Mitigation strategies, such as lighting that mimics natural light, the use of blue light-blocking glasses, and the combination of light and sleep, may represent relevant preventive measures for maternal-fetal health.