That old wives' tale that a sudden emotional shock will send a pregnant woman into premature labor is only slightly off base, a UCLA study on stress during pregnancy says.
Excessive stress during pregnancy can cause premature birth and low birth weight--previously thought to be related solely to the mother's physical condition, UCLA researchers say.
The study also found that stress can cause low birth weight even if the pregnancy is carried full term.
The study is one of the first to document that, independent of a woman's medical risks, stress adversely affects both prematurity and low birth weight, said Christine Dunkel-Schetter, a psychology professor and principal investigator of the study.
The findings raise important questions about how obstetricians view patients' risk factors in pregnancy and what psychological assistance can be extended to pregnant women to reduce America's high rate of premature birth and infant mortality, Dunkel-Schetter and co-investigator Marci Lobel said at the annual meeting of the American Psychological Assn.
"We don't want to alarm women about the effects of stress on pregnancy because every pregnant mother experiences some levels of stress, often without effects on the baby," said Lobel, now at the State University of New York at Stonybrook. "However, it's important to realize that we now have clear evidence that social and psychological factors can have an impact on birth outcomes, and these factors deserve follow-up in further research and treatment."
Health experts have long suspected that stress adversely affects pregnancy and birth weight, but there was little data until now, Dunkel-Schetter said.
UCLA researchers studied 130 pregnant women of diverse ethnic backgrounds during prenatal care at UCLA Medical Center. The women were interviewed an average of seven times using three standard psychological evaluations measuring stress. Researchers also assessed each woman's medical risk of having a baby that was premature, of low birth weight or with health problems.
Conditions such as diabetes, hypertension or drug use by the mother are known to cause prematurity and low birth weight. But the study found that, next to such medical risks, high stress was the second most important factor.
"When trying to determine whether or not a woman is likely to give birth prematurely, doctors often rely most heavily on the mother's medical risk and history," Dunkel-Schetter said. "Medical risk is certainly a significant factor, but stress has comparable impact on the length of pregnancy."
Unlike old movie scripts in which a single, horrendous event sent a woman into labor, the women most at risk in the UCLA study suffered persistent stress, Lobel said.
"Women who felt more anxious, who were more distressed by the events in their lives and who had chronic stress--it is this type of stress during pregnancy that produced prematurity and low birth weight," she said.
Although UCLA researchers expressed surprise that stress could alter a baby's birth weight, there are plausible explanations for the finding. "Women who are under stress are unable to practice good health habits. They might eat less, for example, and be less inclined to take care of themselves," Lobel said.
Biochemical changes could be another cause. Stress is known to increase levels of the hormones epinephrine and norepinephrine in the bloodstream, Lobel said.
"Epinephrine interferes with oxygen and blood flow to the placenta. Epinephrine has been indicated in the onset of labor. So chronic levels of stress and associated high levels of epinephrine may be the culprit," she said.
The study also found that women at high medical risk did not seem to be under any more stress than women with negligible medical risk, Dunkel-Schetter said.
"One reason we think that's true is the women in our study did not seem to be well-informed about their medical risk. They are not being informed or they are not understanding what they are being told in the clinic," she said.
Although physicians closely monitor the condition of a woman with a high medical risk of giving birth early, it is unlikely that many question their patients about stress, Dunkel-Schetter said.
"I think many physicians believe that stress can have adverse effects in pregnancy," she said. "What they do about it, I'm not sure."
Researchers also looked at whether stress affected the difficulty of labor, the baby's Apgar score (an assessment of overall health) and the complications a baby had after birth. Stress during pregnancy did not appear to contribute to any of these.
Many questions remain about how psychological and social factors influence pregnancy, Lobel said. But the topic is of growing interest because of the nation's poor ranking among other industrialized nations in the health of infants.
Each year, about 250,000 babies are born in the United States with low birth weight--less than 5.5 pounds. They are 200 times more likely to die in infancy and have high risks of cerebral palsy, seizure disorders, respiratory problems and lower IQ.
The next generation of studies will focus on physiological indicators of stress, such as monitoring levels of epinephrine in the blood and testing methods to reduce stress and improve birth outcomes, Dunkel-Schetter said.
UCLA researchers are about to begin a three-year study of 1,000 women in three ethnic groups to look for ways to prevent low birth weight. The study will explore the effects of stress, prenatal care and substance abuse on births.