Stress Causes Early Deliveries

Birth rates impacted by natural disaster affects gender ratio

(RxWiki News) It has been established that that stress in pregnant women can lead to premature delivery. But did you know that a severely stressful event can result in more female births? It’s true.

A recent study looked more closely at exactly how stress affects the baby and mother, and whether it influences the sex of the baby.

The most surprising finding: that it could make you more likely to deliver a girl – not because the baby’s gender will change, but because female babies are easier for a mother to carry to term, said New York University researchers.

"While pregnant, try to avoid stressful situations."

Doctors from New York University examined about 600,000 birth certificates of babies born between 2004 and 2006 in Chile. The researchers chose this time frame because they wanted to see how the 2005 earthquake in the city Tatapaca (magnitude 7.9) affected the births.

The information on the birth certificates included: gestational age when the baby was born (whether it was born premature); sex, weight and height of the baby; whether medical attention was required; mother’s age; the mother’s age and her marital status; how many times she had been pregnant before; where the mom lived (which indicated how close the mother lived to the earthquake’s epicenter).

The researchers compared how stress - the earthquake – affected babies in different stages of fetal development. They also were able to see whether the stressor played a factor in determining a baby’s sex, said Dr. Florencia Torche, associate professor of sociology at NYU in a press release.

The team found that women who were in the second or third months of pregnancy and who lived closest to the earthquake’s epicenter had shorter pregnancies and were more likely to deliver a premature baby (before the mom is 37 weeks pregnant), compared to Chilean women who lived in areas far from the epicenter.

Women in their second month of pregnancy delivered 1.3 days earlier, while women in the third month delivered 1.9 days earlier. Among the women who were three months along when the earthquake hit, more than nine in 100 had an early delivery. Usually, this rate would be just 6 in 100, according to the researchers.

They also report that women carrying female babies were more likely to deliver early – nearly a 4% increase for babies in their second and third month of gestation.

It also appears that high stress leads to the birth of fewer males. Usually, out of every every 100 births, 51 will be boys, but the ratio of boys-to-girls declined 5.8%, which resulted in more female births, said Dr. Karine Kleinhaus, assistant professor of psychiatry, obstetrics and gynecology, and environmental medicine at NYU School of Medicine.

How can this new gender ratio be explained?

Earlier studies show that stressed moms are more likely to miscarry a male fetus because they’re usually larger than females and take up more of the mom’s resources.

Or, they may not be able to adapt to a changing environment in the womb the way that female fetuses can, said the researchers.

Dr. Kleinhaus thinks it’s impossible to avoid natural disasters and other stressors in life, but giving women greater access to healthcare can help mothers deal with stress more effectively so that it has a lesser impact on the pregnancy.

This observational study was published in the European journal Human Reproduction.

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Review Date: 
December 9, 2011