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Stress Shortens Pregnancy Length, Number of Boys Born


NEW YORK--A little stress can be healthy, but if you’re pregnant, your exposure to stress can not only shorten the length of your pregnancy, it can also increase the chance you’ll give birth prematurely and that you will give birth to a girl. These effects were observed among women who were stressed during their second and third trimesters of pregnancy.

Stress during pregnancy can have varying effects

Previous research has shown that stress can have a significant and varying impact on women during pregnancy, and on their offspring as well. A study conducted at the University of Colorado at Denver and Health Sciences Center, for example, evaluated the impact of psychosocial stress, social support, and cytokines (protein molecules that regulate inflammatory responses) throughout pregnancy.

The Colorado investigators found that elevated stress during pregnancy was associated with high production of cytokines and increased risk of complications such as premature labor and preeclampsia. In another study, infants born to women who experienced stress during pregnancy were found to have a higher risk of developing asthma later in life.

The new study explored the effect of stress associated with the June 13, 2005 Tarapaca earthquake in Chile on pregnant women. To do so, investigators from New York University examined the birth certificates of all infants born between 2004-2006 in Chile, where more than 200,000 babies are born each year.

Florencia Torche, PhD, associate professor of sociology, and Karine Kleinhaus, MD, MPH, had access to detailed information on each mother and child, including gestational age at delivery, weight, height, sex, and necessary medical attention, as well as where the mother lived at the time of the earthquake, her age at delivery, pregnancy history, and marital status.

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Generally, women who experienced the 7.9-rated earthquake during their second trimester gave birth 1.3 days earlier than women who lived in areas not affected by the earthquake, while those exposed during their third trimester delivered 1.9 days earlier. In Chile, the usual rate of premature birth is about 6 in 100 women, but this rate increased by 3.4% (9 in 100 women) among women who experienced the earthquake in their third trimester.

Exposure to the earthquake appeared to have an impact not only on when women delivered, but the sex of their child. Dr. Kleinhaus, assistant professor of psychiatry, obstetrics and gynecology, and environmental medicine, noted that “Generally, there were more male than female live births.” Compared with the typical ratio of male to female births of 51:49, the investigators saw a change in the ratio, “of 45 male births per 100 births, so that there are now more female than male births.”

Professor Torche noted that “stress may affect the viability of male births.” Indeed, previous research has indicated that stress may cause a miscarriage of a male fetus. Reasons for this may include an inability of a male fetus to adapt to the stress in the womb, and the fact that males tend to grow larger than females, and so are more demanding on the mother.

How can these findings help pregnant women? Torche indicated that their research “suggests the need to improve access to healthcare for women from the onset of pregnancy and even before conception.” While this will not reduce a woman’s exposure to stress in her life, “it may provide care, advice, and tools that would allow women to cope with stressful circumstances.”

Coussons-Read ME et al. Brain, Behavior and Immunity 2007 Mar; 21(3): 343-50
New York University

Picture credit: Wikimedia Commons