Stress During Pregnancy Is Bad for Boys

During times of stress, a pregnant woman's body is able to independently cull weak, less viable male fetuses, reports the journal Proceedings of the National Academy of Sciences.

It is known that during periods of adversity and disaster, particularly after natural disasters, fewer boys are born. Male fetuses and embryos are generally less viable than female fetuses and embryos, but the reason why a woman's body rejects weak male fetuses and miscarriages occurs remains unclear.

Researchers from the University of California analyzed a database of newborns in Sweden from 1751 to 1912.

At the beginning of the study, there were two different theories explaining why in stressful situations there is a noticeable change in the ratio of the number of newborn girls and boys, in which the proportion of the latter noticeably decreases.

The first theory suggests that, in response to stress, the mother’s body begins to involuntarily damage the fetus, and the weaker male fetuses suffer most seriously from this. This is why women are more likely to experience spontaneous miscarriages of boys.

However, there is a second theory, according to which, in stressful situations, the mother’s body becomes less tolerant (tolerant) of embryos and fetuses that have any abnormalities or diseases. The fetus, which would have a chance to be born under favorable conditions, dies under stress.

An analysis conducted by American scientists confirmed the second theory. If the first theory were true, then stress would lead to various damage to the fetuses and boys who survived pregnancy would be born with certain damages. As a result, their life expectancy should be shorter than that of males born in more favorable periods.

However, researchers have found the opposite - boys born during stressful times live longer on average than boys born during more favorable periods.

Thus, the body of a pregnant woman selectively damages only those male fetuses that are initially less viable, allowing stronger individuals to survive. Scientists have suggested that nature, which gives only strong and healthy babies a chance to be born, increases a woman’s chance of preserving her genetic information.