Birth deterrent: stress hormone cited in early miscarriages.

High concentrations of a stress hormone in newly pregnant women might make them more likely to have miscarriages, a new study finds.

Roughly 30 to 50 percent of pregnancies end in miscarriage, says biologist Pablo A. Nepomnaschy of the National Institute of Environmental Health Sciences in Research Triangle Park, N.C. That number is imprecise because many miscarriages occur within days of conception, before a woman knows that she is pregnant. Miscarriage is a natural process that evicts defective embryos that are unlikely to survive, Nepomnaschy says, but the high rate suggests that other factors also play a role.

A few previous studies examined the relationship between miscarriage and stress, but their results were inconsistent. Nepomnaschy focused on extremely early pregnancies in healthy women and measured a biochemical indicator of stress.

In high-stress circumstances--for example, energy deficit, infection, injury, or social conflict--the body's adrenal gland produces more of the hormone cortisol. To test whether cortisol concentrations are associated with miscarriage, Nepomnaschy enlisted 61 married women in rural Guatemala who weren't using birth control. Over a year, each woman collected a urine sample every other morning right after she woke up. Nepomnaschy and scientists at the University of Michigan in Ann Arbor used these samples to assess each woman's pregnancy status and cortisol concentration.

There were 22 pregnancies during the study. In 9 of 10 pregnancies in which a woman's cortisol concentrations had jumped above her personal average during the first 3 weeks of gestation, a miscarriage resulted. Of the 12 pregnant women whose cortisol concentrations stayed at or below average during these first few weeks, only 4 miscarried, Nepomnaschy and his colleagues report in an upcoming Proceedings of the National Academy of Sciences.

The miscarriages in the study occurred an average of 2 weeks after conception. "These findings are eye-opening, suggesting that elevated cortisol levels in early pregnancy [pose] a nearly complete threat to the pregnancy continuing," says endocrinologist David H. Abbott of the University of Wisconsin-Madison. However, he says, it's not dear whether outside stressors or some biologic process intrinsic to early pregnancy in certain women caused the increase in cortisol.

He notes that some research suggests that cortisol can suppress progesterone, a hormone essential to a successful pregnancy.

Petra Arek, a physician at Charite, an institute at the University of Medicine in Berlin, says that the study complements her observations that stress can adversely affect pregnancy. That earlier work, however, concentrated on women later in their first trimester and determined stress on the basis of the women's self-reports rather than on cortisol measurements.

"Although looking at slightly different time points during pregnancy, we both came to the same conclusion" Arck says. High stress during pregnancy disrupts normal endocrine functioning and interferes with fetal survival, she proposes.

Nepomnaschy agrees that maternal stress remains the simplest explanation for his results. He briefly interviewed the women in his study three times a week. He's still analyzing those interviews, which might reveal whether outside stressors brought on the higher cortisol concentrations, he says.