Studies Affirm That Boy Fetus Vulnerable To Stress

After the terrorist attacks of Sept. 11, 2001, there was a small but actual rise in the number of miscarriages across the country -- especially for women who were pregnant with boys.

The finding adds to confirmation that boys are more vulnerable to stress than girls while in the womb. The study also affirms that the tragic events of 9/11 intensely affected people far beyond the limits of New York City.

"The stress of a mother affects the fetus, and it's not just these individual stressors like whether you had a divorce or lost your job, but also these ambient stressors, like the economy and September 11," said Tim Bruckner, a population health researcher at the University of California, Irvine. "The effects resonated across the whole society. We were fundamentally bereaving what we saw on TV."

In the United States an average of 105 boys are born for every 100 girls. But in times of stress, like after natural disasters or economic subside, studies have shown that the ratio drops, and fewer boys are born than expected. So far, it hasn't been clear why.

One theory is that stress harms sperm that bear Y-chromosomes. It could also be that people just have less sex during stressful times, which might favor girls. Or perhaps something happens during pregnancy to influence the birth ratio.

The tendency of an tremendously anxious woman to miscarry male babies might have developed in our ancestors as a way to maximize the number of grandchildren she would eventually have, Bruckner said.

When times were flush and food plentiful, the theory goes, women could pour more resources into their rising sons, boosting the chances that they would go on to become alpha males. In many mammals, including red deer, alpha males are more probable to find mates and have babies.

If conditions turned sour during a pregnancy, on the other hand, it might be fine for a woman to miscarry a male baby and try again next year when life is less stressful.

The new study doesn't offer any clear advice to pregnant women about how to avoid miscarriages, Bruckner said. Instead, it highlights one of the ways that collective stress can impact the health of our nation at its core.