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Does the moon play a role in childbirth?

The most recent, exhaustive studies suggest that there is no relationship between the different lunar phases and birth rates

Una mujer embarazada, a la luz de la Luna
A pregnant woman in the moonlight.Daniel Balakov (Getty Images)

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There is a long-standing belief that there is a connection between the Moon, fertility and birth. It’s true that, on average, the menstrual cycle lasts 28 days; a period similar to that of the lunar synodic month, the term for the 29 days between identical lunar phases. That duration also resembles the sidereal month, as are called the 27 days that it takes the Moon to complete its orbit around the Earth. True too, the average length of pregnancy (post-conception) is 265 days, which is equivalent to nine lunar synodic months.

Studies conducted in the 1970s and ‘60s seemed to show a relationship between the lunar phase cycle and an increase in births; however, those studies did not reach a consensus about which lunar phase was influencing birthrates. More recent studies have now been carried out that have failed to find any relationship between the different phases of the Moon and an increase in birthrates.

One of these studies was published in 2004 by the influential American Journal of Obstetrics and Gynecology. That investigation precisely analyzed the influence of the lunar cycle on birthrates by studying data from 664,039 North Carolina childbirths.

Its researchers compared birthrates during the eight phases of the lunar cycle: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter and waning crescent. In addition, it specifically analyzed whether the lunar phases affected the total number of births among different groups: spontaneous onset deliveries, multiparous deliveries, instrumental deliveries, Cesarean sections and instances in which there were complications including premature rupture of membranes and preterm deliveries. The results of this comprehensive study showed that there were no significant differences in the total number of deliveries nor in any of the groups that were analyzed.

Spain has also conducted studies on the subject. Two have been published recently: one that was quite interesting and was carried out by Francisco José Marco-Gracia analyzed 23,689 births that took place between 1810 and 1929. All had taken place in rural areas, had been vaginal and free from medical intervention. That study likewise failed to find any relationship between the lunar phases and birthrates. Another study, which was also quite interesting, was directed by Félix Morales and published in 2020 and analyzed births in Valladolid between 2015 and 2018, and likewise did not find any relationship between birthrates and lunar phases. That study also analyzed various meteorological phenomenon, with which no significant relationship was encountered.

And so, the answer to the question is that no scientific evidence has indicated that a full moon (or any other lunar phase) provokes an increase in births. I will note that, as an obstetric professional, when we are busy at work with many childbirths, there is a tendency to blame it on the Moon. But there is a simple explanation for that phenomenon: when we are overseeing many births, or rather, when there is much pressure to provide care, it’s easy to look at the sky and, if there is a full moon, remember the fact. If the moon isn’t full, you tend to forget you looked at the sky in the first place. But when we’re overseeing few births, no one looks at the sky nor establishes an association with the current lunar phase.

Ana Palacios Marqués is head of obstetrics at the Hospital General Universitario Dr. Balmis in Alicante, Spain.

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