Can a full moon cause a woman to go into labor?

As a full moon approaches, I am convinced that more of my patients will go into labor. Of course as a scientist this can be hard to explain and yes I have been proven wrong on many full moons. However, for the most part the number of people breaking their water bags early or simply going into spontaneous labor seems to be higher depending on the lunar calendar according to the nurses and doctors who work the labor and delivery shift at night.

My personal belief of lunar effects on labor is something that is commonly shared among nurses working the night shift in hospitals. Most of us have the habit of looking up to the sky to see where the moon is prior to starting a night shift rotation at the hospital. Besides, the lunar role in obstetrics, there are many facets of our society that seem to be under lunar control. For instance, conception and fertility have also been linked to moon phases; and then there are the entirely non-pregnancy related behaviors, like homicide rates, suicide rates, emergency room admissions and outbreaks of insanity. Supposedly, all of these things increase on a full moon.

It’s called the lunar effect, and, as far as births are concerned, the primary explanation for the effect focuses on the moon’s gravitational pull. It basically states that much the way the moon’s gravity controls the tides, it can control a woman’s body. The human body is 80 percent water, after all. And, given that both menstruation and ovulation roughly follow a lunar cycle — occurring on a monthly basis — it doesn’t seem too far off to think that the moon could have a say in childbirth as well.

In this blog entry, I am going to explore the evidence on both sides of the argument and allow you to determine if the lunar calendar affects pregnancy labor.

If you ask around most hospitals, you will hear especially from the night shift labor and delivery nurses that labor and lunar cycles go hand in hand. Although we all love to trust and believe our nurses, these are verbal anecdotal stories based on their own experiences and not evidence based.

However, there is some substantial studies that have been performed looking at just this “myth” . A 1959 study broke the month into consecutive three-day periods and found that the three days of a “full moon window” — the day before, day of and day after a full moon — had more births than any other single three-day period [source: Shulman]. Another study, this one published in 1966, studied birth rates by moon phase — full, half, one-quarter and three-quarter. The authors found that within the study period, more births centered around the full-moon phase than any other.

Although these studies seem promising and convincing, they are more of an anomaly then the norm. Most studies that have been repeated in order to justify a link between lunar cycle and labor have failed to do so. For instance, the following study is one of many in the data base. In 2005: Looked at 564,039 births in North Carolina between 1997 and 2001 and found “no predictable influence of the lunar cycle on deliveries or complications” This study is comprised of a large data pool and certainly renders enough statistical power to disprove those prior single center studies.

So, where does that leave us?

I personally believe that although studies have not been able to correlate the two, there is something mystic and perhaps logical about a myth that deals with lunar effects and gravitational pulls and the higher incidence of births. Perhaps, I practice cognitive bias and only take of notice of higher birth rates when the moon is full.

It is also important to explain some important misconceptions in regards to certain aspects of the moon. I made reference to them in the early part of the blog as an example of some of the commonly pointed out facts. For instance, a full moon really only lasts an instant and not the three days described in the earlier study I pointed out are not a reality. Also, people like to reference the moons gravitational pool on the body but most studies have shown this phenomena to be extremely weak and as far as the full moons gravitational forces on the tides, well, again science has shown us that it is actually a function of how far the moon is from earth at any given time and not related to the phases of the moon cycle.

So I hope that this myth buster was both relevant and educational.

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