The Impact of Lunar Phases During Day and Night Cycles on Perinatal Outcomes: A Nationwide Cohort Study

Light changes during the lunar cycle affect rhythms in diverse species. Human studies focusing on whether the moon influences human health have so far neglected the effects of light/dark cycles. The purpose of this study was to investigate whether lunar phases impact perinatal outcomes by considering illumination levels due to day/night rhythms.

To assess the influence of moon phases, this nationwide cohort study identified cases with a singleton pregnancy that involved daytime (06:00 a.m. to 08:59 p.m.) and nighttime (09:00 p.m. to 05:59 a.m.) delivery at ≥ 23 + 0 gestational weeks with a birthweight of ≥ 500 g. Data on women who underwent elective cesarean or labor induction were excluded from the analyses. The lunar cycle was categorized as full moon, new moon, or other lunar phases. The standardized birth ratio (SBR) was chosen as the primary outcome parameter, while the duration of labor and adverse neonatal short-term health (pH of < 7.2 and/or a 5-min Apgar score of < 7) were chosen as the secondary outcome variables.

We identified a total case number of 462,947 births, of which 242,518 (52.4%) occurred during the day and 220,429 (47.6%) at night. Different moon phases did not appear to influence either the SBR or adverse neonatal outcomes. However, nighttime births may show a trend toward a prolonged maximum duration of labor related to moon phases (62 vs. 65 vs. 70 h for new/full/other moon phases, p = 0.05).

Considering illumination levels, some moon phases may increase the risk for prolonged births during nighttime. However, assessing the effect of lunar phases on health variables is complex. Co-environmental agents should be incorporated into future analyses.