Mom's stress may affect early child development

By Beth Azar
Monitor staff

How women deal with stress during pregnancy and after giving birth is strongly associated with fetal and infant development, according to data presented at APA's 1999 Annual Convention, Aug. 19 - 24 in Boston.

In particular, stress and anxiety during pregnancy is associated with low birth weight and early delivery, said Christine Dunkel-Schetter, PhD, of the University of California-Los Angeles. And Ann Marie Yali, PhD, and her colleagues find that optimists seem to elude stress during pregnancy by maintaining a sense of control over the situation. In turn, Dunkel-Schetter with colleagues at the University of California at Irvine recently published data indicating that both stress and optimism determine birth outcomes such as the time of delivery and the baby's birth weight. In contrast, Marci Lobel, PhD, and her colleagues at the State University of New York at Stonybrook have preliminary findings that optimism, not stress, predicts adverse birth outcomes and that it just so happens that optimistic women are less stressed.

Even after a baby is born, parents' and other caregivers' expectations about the baby's health can play a decided role in the child's development, said Marilyn Stern, PhD, of the University of Albany. She and her colleagues find that parents and health-care providers develop a stereotyped view of premature babies that affects how they treat infants. It may have adverse effects on cognitive development, her study found.

Stress and birth

In her invited address "Is maternal stress a risk factor for adverse birth outcomes?" UCLA's Dunkel-Schetter summarized research she and her colleagues have conducted over the past several years.

One main finding has been that women under high stress during pregnancy are as much as four times more likely to deliver their babies prematurely than women who experience little stress.

To find out what might trigger preterm labor in these women, the researchers examined levels of corticotrophin-releasing hormone (CRH) during pregnancy. The hormone is known to be a major regulator of the stress response.

Under normal stress, the hypothalamus releases CRH, which triggers the release of another hormone, ACTH, which in turn leads to release of cortisol from mothers' adrenal glands. Cortisol, in turn, shuts off the further release of CRH and the stress response.

By a still undetermined pathway, this system is not shut off but instead is progressively activated during pregnancy: Levels of the stress hormones, including CRH, gradually increase at different rates in different women, determining the time of labor and delivery.

Studies find that women who deliver premature babies have much higher levels of CRH--as early as 18 weeks into their pregnancy--than women who carried their babies to term, said Dunkel-Schetter. In fact, researchers have begun to believe that CRH works as a "clock" to determine the timing of delivery, she said.

She and her colleague, Calvin Hobel, MD, of Cedars Sinai Medical Center in West Los Angeles, now have preliminary data indicating that maternal stress increases CRH very early in pregnancy and can predict and possibly precipitate early delivery.

"In women who had preterm [babies] there was an association between psychological distress at 18 weeks and CRH at 28 to 30 weeks," she said. Though not well tested, one theory holds that stress may also play a role in preterm delivery and low birth weight by putting women at increased risk of bacterial infection that can lead to early delivery.

And several studies show a link between stress and unhealthy behaviors, such as smoking, drug use and poor prenatal care that are related to low birth weight, said Dunkel-Schetter.

Her team also found that a person's emotional response to stress, rather than the stressful events per se, are most responsible for affecting birth outcome, said Dunkel-Schetter.

And, she said, "Strong anxiety about pregnancy may pose the greatest risk of early delivery."

Positive thinking

A woman's level of optimism--which is generally defined as having positive expectations--may have a big effect on how anxious she is about her pregnancy, postulated the University of Pittsburgh's Yali, who co-chaired with Lobel the symposium "Adaptation to reproductive health events--the impact of expectations."

In two studies of the relationships between optimism, perceived control, coping and psychological distress, Yali, Lobel and their colleagues at the State University of New York at Stony Brook found that optimism was associated with less distress.

Driving this relationship was a tendency for optimistic women to use coping skills other than avoidance, which includes avoiding people in general, trying not to think about the birth and sleeping to escape problems.

"Optimists were less likely to use avoidance," said Yali. "And those who did not use this way of coping were protected from distress."

Optimists were also more likely to believe they have control over the outcome of their pregnancy, and with this sense of control tend to be less distressed. In addition, optimism had a "powerful" independent effect on emotional distress, said Yali.

"These studies reveal that there is power in positive thinking," she said.

In another study presented last March at the Society of Behavioral Medicine Annual Meeting, Lobel and her colleagues found that optimism predicted length of pregnancy and therefore birth weight. Less optimistic women delivered earlier and had lower weight babies than their optimistic counterparts after controlling for health behaviors, such as smoking and diet, and medical risks such as diabetes and history of miscarriage.

And when the researchers controlled for optimism, stress no longer predicted birth outcome, says Lobel. In contrast, a study published by Dunkel-Schetter and her colleagues in the July Health Psychology (Vol. 18, No. 4, p. 333 - 345) indicates that optimism predicts birth weight, after controlling for timing of delivery, but that stress is still important, predicting the timing of delivery. The jury is still out on whether stress levels or positive thinking are more important, say the researchers.

Stereotyping preemies

Negative thinking can have its own effect on child development, said the University of Albany's Stern at the same symposium. Over the past 15 years, she, Katherine Karraker, PhD, of West Virginia University, and their colleagues have examined people's expectations about premature babies and ways those expectations can affect children's development over time.

Although premature babies are often initially less responsive and socially active than full-term infants, at about nine months, most healthy preemies look no more vulnerable than their full-term peers.

Despite that, in several studies Stern and her colleagues found that when mothers, college students, nurses and medical students view a videotape of a 9-month-old baby who is labeled premature, they think less of the infant than if the same infant is labeled full-term. They say that the infant looks physically less mature, weaker, less sociable, cognitively less competent, and behaviorally less mature, and is less liked--a trend Stern and Karraker call "prematurity stereotyping."

In addition, when given an opportunity to interact with a 5-to-7-month old infant labeled by the researchers as "premature" or "full-term" regardless of its actual status, mothers of both full-term and premature babies treat infants labeled as "premature" more negatively--they hold them and touch them less than babies labeled full-term, said Stern.

She and her colleagues also have preliminary data from a pilot study in which they followed mothers and their infants for several years, comparing the degree mothers stereotype their premature babies to the babies' degree of development. They first rated mothers' general degree of prematurity stereotyping, then videotaped them interacting with their infants at 5 months, 9 months and 12 months.

When asked which of three toys was most appropriate for their infants, mothers of premature infants consistently chose a more "immature" toy than mothers of full-term infants. In addition, the more negative a mother's score on the prematurity stereotyping scale, the less she interacted with her infant by touching, active play and engagement--what Stern terms "positive parenting."

To test the long-term consequences of prematurity stereotyping, the researchers followed up with mothers when their children were 2-and-a-half and 3 years old.

They found that children showed less cognitive development if their mothers had shown greater levels of prematurity stereotyping when their children were 5 months old. High levels of stereotyping were also related to more protective parenting, while lower levels were related to whether mothers interacted with their babies in a more positive way.

"Clearly," said Stern, "the preliminary results suggest a long-term relationship between early maternal expectations of vulnerability--including prematurity stereotyping--and later child developmental outcomes."Y



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