New study finds stress during pregnancy can impact baby's sex

By Felicite Fallon
November 11, 2019

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Catherine Monk, PhD

Catherine Monk, PhD, Professor of Medical Psychology in the Departments of Obstetrics & Gynecology and Psychiatry at NYP/CUIMC

A new study, led by researchers from NewYork-Presbyterian/Columbia University Irving Medical Center, identifies the types of physical and psychological stress during pregnancy that can have the greatest impact on fetal and child development.

The study was published in the journal PNAS, the Proceedings of the National Academy of Sciences.

“The womb is an influential first home, as important as the one a child is raised in, if not more so,” says study leader Catherine Monk, PhD, professor of medical psychology at Columbia University Vagelos College of Physicians and Surgeons and director of women’s mental health in the Department of Obstetrics & Gynecology at NewYork-Presbyterian/Columbia University Irving Medical Center.

In the study, Monk and her team examined 27 indicators of psychosocial, physical, and lifestyle stress collected from questionnaires, diaries, and daily physical assessments of 187 otherwise healthy pregnant women, ages 18 to 45.  

One of the study’s major findings suggest that pregnant women experiencing stress, whether physical or psychological, are less likely to have a boy. But in this study, the sex ratio in the physically and psychologically stressed groups favored girls, with male-to-female ratios of 4:9 and 2:3, respectively.

The study’s findings are supported by other historical instances of decreases in male births.

“Other researchers have seen this pattern after social upheavals, such as the 9/11 terrorist attacks in New York City, after which the relative number of male births decreased,” says Monk. “This stress in women is likely of long-standing nature; studies have shown that males are more vulnerable to adverse prenatal environments, suggesting that highly stressed women may be less likely to give birth to a male due to the loss of prior male pregnancies, often without even knowing they were pregnant.”

Learn more about the study here, or read the full publication on PNAS.

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