Stress Hormone Levels Predict Length Of Gestation In Human Pregnancy

October 14, 1998

Levels of a stress hormone, corticoptropin-releasing hormone (CRH), measured in mothers in the early third trimester of pregnancy may predict the length of gestation and preterm delivery, according to a study by a University of Kentucky researcher working in collaboration with scientists at the University of California, Irvine. The findings are reported in today's American Journal of Obstetrics and Gynecology.

Previous studies have implicated maternal stress as an important risk factor of prematurity-related outcomes, such as preterm birth and low birthweight. CRH, a hormone released primarily in the brain, is known to play a central role in regulating the body's hormonal and immune responses to internal and external challenges, including stress. During pregnancy, CRH is also synthesized in large amounts by the placenta and is released into maternal and fetal circulatory systems.

In previous studies, elevated levels of maternal CRH have been associated with the presence of medical complications in pregnancy and with preterm labor. It was not clear, however, whether CRH was a marker of complications or whether the CRH played a role in influencing the timing of onset of labor.

Researchers sought to determine whether elevated levels of CRH were a predictor of preterm labor and delivery, and if the effects of CRH on the timing of delivery were independent from those of medical complications during pregnancy.

"Our results indicated that women with higher CRH levels at 28 to 30 weeks gestation delivered earlier and were more likely to deliver preterm," said Pathik D. Wadhwa, M.D., Ph.D., assistant professor of behavioral science, obstetrics and gynecology, and psychology, UK College of Medicine.

Sixty-three pregnant women had blood drawn during the early third trimester - 28 to 30 weeks of gestation. Blood samples were measured for CRH and medical risk factors for prematurity were assessed from the women's medical records. The women were divided into groups based on presence or absence of spontaneous labor and the presence or absence of medical conditions that placed them at risk for preterm delivery.

Study results indicated that although women in the high-risk group had higher CRH levels, among women who delivered following spontaneous labor, the effects of maternal CRH levels on preterm delivery were statistically independent of those from medical risk. Among women who delivered following induced labor or cesarean delivery, maternal CRH levels were not an independent predictor of preterm delivery, but predicted preterm delivery via their association with medical risk.

Preterm birth is one of the most significant problems in maternal-child health in the United States today, Wadhwa said. It is the leading cause of perinatal mortality and morbidity, and has a high incidence in the United States - 10 percent of all births, the highest rate in all developed nations. Although advances in medical technology have improved survival, the rate of preterm delivery has not decreased in 40 years.

Wadhwa believes the study results indicate that placental CRH is potentially implicated in the timing of human delivery in at least two ways. First, placental CRH may play a role in the timing of onset of normal labor. Early or accelerated activation of the placental CRH system may, therefore, result in earlier onset of spontaneous labor and delivery. Second, placental CRH also may be a marker of medical risk conditions for preterm delivery, and therefore may be an indirect predictor of earlier delivery.

Wadhwa and colleagues are continuing research at the University of Kentucky and the University of California to examine the effects of elevated maternal CRH levels and the rate of change of those levels during pregnancy as a predictor of prematurity and other adverse fetal and infant developmental outcomes. The study was funded by the National Institute of Child Health and Human Development at the National Institutes of Health.

University of Kentucky Medical Center

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