By Amy Norton
Over a 10-year period, the researchers found that of more than 19 000 Danish women who were pregnant those who reported high levels of psychological stress were 80 percent more likely to suffer a stillbirth than women with low stress levels.
Most women with high stress levels did deliver a healthy baby, with the stillbirth rate being just under five percent. However, women with low or moderate stress levels had a stillbirth rate of about three percent, the researchers report in the medical journal BJOG.
This is the first study to establish a link between psychological stress and stillbirth, so it's too soon to conclude that stress causes foetal deaths, lead researcher Dr. Kirsten Wisborg told Reuters Health.
"Our result should be confirmed by other studies," said Wisborg, of Aarhus University Hospital in Denmark.
If heavy stress is confirmed as a risk factor for stillbirth, she noted, then it will be necessary to see whether stress reduction can lower the risk.
The researchers based their findings on data from 19 282 women who were scheduled to deliver a single infant at their hospital between 1989 and 1998. The women completed several questionnaires during their pregnancy, including a standard measure of psychological stress that they completed before their 30th week of pregnancy.
The questionnaire also asked them about their stress levels in the past month - gauging, for instance, how often they had felt unhappy, worried or unable to deal with their problems.
Wisborg's team found that women with high stress scores were more likely to be smokers or to have been overweight before pregnancy than women with low stress levels; they were also less educated overall and more likely to be single.
However, even with these factors taken into account, high stress alone was linked to an 80 percent higher risk of stillbirth.
Wisborg said she could only speculate on the reasons. One possibility is that chronically high stress hormones play a role.
For example, Wisborg noted, stress, depression and anxiety all trigger the release of catecholamines, a group of hormones that includes dopamine and epinephrine (adrenalin). Animal research suggests that high levels of these hormones may hinder blood flow to the placenta.
However, Wisborg pointed out, it is also possible that women under heavy stress differ from less-stressed women in their lifestyle habits, which might explain the higher stillbirth risk.
Further studies are needed to sort these questions out, she said.