Ask A Scientist© Zoology Archive

name       Paul
status     other
age        20s

Question - Can the moon affect a woman's pregnancy?
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There is some evidence that the lunar cycle affects human behavior so it
would not be a stretch to posit some effect on pregnancy... to what extent I
do not know.

PF
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All you have to do is to discuss this topic with a OB doctor or nurse and they
will respond very quickly in the affirmative when it comes to delivery.  The
busiest time for pregnancy termination is clearly more frequently around a
full moon.  Whether this is due to a physical or mental factor has yet to be
determined.
 
sds
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up-date July 2008
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There is no scientific evidence of the moon's phase affecting the timing of birth, 
or conception, or any other aspect of pregnancy.  We can look at this from several 
angles.
First, asking an OB nurse is not a reliable method to arrive at the answer. There 
is the problem of "confirmation bias", which is to say you're less likely to notice 
pregnant mothers when the moon is *not* full if you already suspect there is some 
correlation (in a similar manner, if you buy a certain car, you are much more 
likely to notice other people driving that same model).  Next, according to Dr. 
Michelle Hakakha, M.D., there may indeed be more pregnant mothers admitted and 
presenting contractions during full moons, but they don't end up *delivering*. She 
denies any increased deliveries during a FM.
Second, many authoritative sources, such as Harvard Health Publications state that 
the moon-pregnancy link is a myth.
Third, in 1985, Rotton and Kelly did a meta-study of 37 other studies on the moon's 
effect on crime, psychiatric admissions, etc., and found no more than .03 % 
correlation, which is essentially zero (less than the background variation).
Fourth, and most importantly, there are several persistent misunderstandings about 
the moon's effect on tides and other bodies...
A.) The moon has no preferential attraction to water.  The fact that we are made 
largely of water is irrelevant.
B.) The moon only affects the ocean tides because of the differential distance 
between two sides of the earth. The moon pulls more strongly on the near side of 
the earth because it is measurably closer.  This effect becomes essentially zero 
for bodies as small as ours.  To demonstrate this, you might ask yourself why you 
don't see tides going up and down in very large lakes.
Lastly, there is a constellation of beliefs involving women's reproduction system 
and the moon. This is partly fueled by the observation that a woman's menstrual 
cycle averages 28 days (although it can vary widely) and the moon's cycle is 29.5 
days, which is another example of confirmation bias (the cycle does *not* sync 
with the sun or other planets or seasons, sunspot activity, etc., but no one 
notices that). This similarity is probably just coincidence, because in nature we 
find all sorts of days in a menstrual cycle that most people don't notice: 
opossum = 28, guinea pig = 11, sheep = 16, sows = 21, macaque monkeys = 25, 
chimpanzees = 37, rats and mice = about 5.

Paul Bridges
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