Women who exhibit signs of stress are three times more likely to miscarry during the first three weeks of the pregnancy, a recent study of a small population of women found.

Pablo Nepomnaschy and a group of University of Michigan researchers measured the cortisol levels—a stress induced hormone—in urine samples taken three times weekly for a year from 61women in a rural Guatemalan community. Nepomnaschy conducted the fieldwork while he was a doctoral student at U-M both at the Anthropology Department and the School of Natural Resources and Environment. He is now a post-doctoral fellow at the Epidemiology Branch of the National Institute of Environmental Health Sciences.

The Guatemalan study is the first known study to link increases in cortisol levels to very early-stage pregnancy loss.

According to previous scientific reports, anywhere from 31 percent to 89 percent of all conceptions result in miscarriage. Most studies begin when women notice they are pregnant, about six weeks after conception. Most miscarriages, however, are known to happen during the first three weeks of pregnancy.

“The only way to capture the first three weeks of pregnancy is to begin collecting their urine from before they become pregnant. That is extremely labor intensive and expensive,” Nepomnaschy said.

In the Guatemalan study, 22 pregnancies occurred in 16 women, and each woman’s cortisol levels were measured against their own baseline levels. Researchers found that 90 percent of women, whose ages ranged from 18 to 34, with elevated levels of the stress-induced hormone miscarried during the first three weeks of pregnancy, compared to 33 percent of those with normal levels.

The body may recognize the elevated cortisol levels as an alarm that conditions are unfavorable for pregnancy.

“Maybe increased cortisol is understood by the body as a cue that the context is uncertain, changing, or the quality of the environment is deteriorating,” Nepomnaschy said. “The body’s response is to stop any extra activity and go back to its most basic functions.”

Given that previous studies focus on later pregnancy stages did not find an association between elevated cortisol and miscarriage, Nepomnaschy and colleagues speculate that stress may be more likely to lead to loss during the earliest stages of pregnancy, while the embryo is just beginning to develop. They caution, however, that more research is necessary on this topic before definitive conclusions can be reached.

It’s unclear if cortisol is directly involved with the miscarriages or if it signals some other mechanism in the body that causes the miscarriage. However, the results are consistent with a 2004 study in which Nepomnaschy his colleagues found that elevated cortisol levels were associated with lower progesterone levels—a hormone that prepares the uterus for the implantation of the fertilized ovum.

“The two pieces of research are consistent in this sense,” Nepomnaschy said.

The next step, Nepomnaschy said, is to attempt to replicate these results in a larger population.