During early pregnancy, miscarriage may be more likely among women with high levels of the stress hormone cortisol, according to a study published online in the Proceedings of the National Academy of Sciences .

Maternal stress is often considered a risk factor for miscarriage, yet data supporting this association are lacking, noted lead author Dr. Pablo A. Nepomnaschy, from the National Institutes of Health (NIH) in Research Triangle Park, North Carolina.

The NIH team evaluated 61 women aged 18-34 over 12 months in a small community in rural Guatemala, collecting each woman's urine three times a week to check for pregnancy status and levels of cortisol, a stress-linked hormone.

Over the year, 16 of the women had 22 pregnancies. Nine pregnancies were carried to term and 13 were lost. Among the findings:

—Miscarriages were 2.7 times more likely among women with increased cortisol levels.

—Miscarriages happened after an average of about two weeks of pregnancy.

—90 percent of women with high cortisol levels miscarried in the first three weeks of pregnancy.

—33 percent of women with normal cortisol levels miscarried in the first three weeks of pregnancy.

Dr. Nepomnaschy said it's unclear why a boost in cortisol might raise miscarriage risks, but he offered a hypothesis that "the body might interpret that as conditions deteriorating, and maybe that might trigger an abortion mechanism."

"Try to provide yourself with what you consider a good environment. The less stress, the better," he suggested.