December 7, 2004
Tracking Stress and Depression Back to the Womb
By LAURIE TARKAN
By listening intently to movements and heartbeats, researchers are finding that the fetuses of
mothers who are stressed or depressed respond differently from those of emotionally healthy
women.
After birth, studies indicate, these infants have a significantly increased risk of developing
learning and behavioral problems, and may themselves be more vulnerable to depression or
anxiety as they age.
The studies, researchers caution, are preliminary. Stress or depression during a mother's
pregnancy is only one among many influences that affect an infant's development. Even among
mothers who are depressed or highly stressed, the rate of emotional and behavioral problems in
children is still very low.
"The last thing pregnant women need is to have something else to worry about," said Dr. Janet
DiPietro, a developmental psychologist at the Johns Hopkins University Bloomberg School of
Public Health.
The studies reflect growing evidence that stress and depression can have early and lasting effects
on a child's life.
If the findings hold up, experts say, they could eventually lead obstetricians, midwives and other
health professionals who care for pregnant women to include mental health screening as a routine
part of prenatal examinations. Such screening could allow doctors to recommend therapy or
treatment for pregnant women who suffer from depression or other disorders.
"We could be intervening earlier," said Dr. Catherine Monk, an assistant professor in the
psychiatry department at the College of Physicians and Surgeons at Columbia. "Prenatal care is
an optimal time to do mental health screening, but we don't."
The effects of stress on a fetus have been well documented in animal studies. In rats, researchers
have found, babies born to stressed mothers show permanent changes in brain chemistry and
behavior. For example, rat pups exposed prenatally to elevated levels of the stress hormone
corticosterone were born with reduced numbers of corticosterone receptors in the brain, and the
animals showed exaggerated responses to stress.
In humans, there is convincing evidence that mothers who are stressed in pregnancy are more
likely to give birth to preterm or infants with low birth weights.
In recent years, scientists have begun to home in on more subtle effects, studying how unborn
fetuses respond to their mothers' anxiety or depression, the emotional health of the infants after
birth and how they fare later in childhood. Some studies have offered unusual glimpses into the
symbiotic relationship between a mother and a developing child.
Dr. Monk has looked at the increase and decrease in a fetus's heart rate when its mother is under
stress.
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In one study, women who were in the third trimester of pregnancy went through psychological
screening for depression and anxiety. They were then asked to perform a series of stress-inducing
computer tasks. As expected, all the women showed increases in heart rate, respiration and blood
pressure. The responses of the fetuses were more varied. The fetuses of mothers who were
depressed or had anxious personality styles showed increases in heart rates. In contrast, the heart
rates of fetuses whose mothers were emotionally healthy showed no fluctuations.
Dr. Monk said the fetuses were not simply mimicking their mothers' responses.
"What this leaves us with is another interpretation," she said. "The fetuses of depressed or high
anxious women are more reactive to stimuli than other fetuses."
She compared the fetuses' responses to the way people in a waiting room might react differently
to a door being slammed. In this case, a fetus might be reacting to the mother's increased
heartbeat or breathing, or to a jolt of stress hormones.
Dr. Monk said depressed women tended to have more difficulty handling stress, which leads to
higher levels of stress hormones like cortisol. She speculated that those higher levels, in turn,
might make the fetus more jumpy.
"My hypothesis is that over the course of gestation, they have been exposed to an altered in utero
environment, which includes increased levels of stress hormones," Dr. Monk said. "This may
make fetuses more susceptible to stressors in the future, and by extension, because stress plays a
role in the development of depression, may make them more vulnerable to depression in the
future."
Though stress and depression are closely intertwined, researchers believe that stress is the more
potent player in affecting prenatal development. In a study by Dr. DiPietro, pregnant women who
perceived their lives, and in particular their pregnancies, as stressful, had fetuses who were more
active in an ultrasound test.
Other studies have linked higher levels of stress hormones in the mother with a more active fetus.
Dr. DiPietro has found that more active fetuses tend to become more active 1-year-olds,
providing some evidence that the effects are not transient.
In newborns, researchers have also found that the effects of a mother's depression lingered.
A study published this year in Infant Behavior & Development compared 70 depressed pregnant
women with 70 women who were not depressed. The study found that compared with the infants
of the healthy mothers, the newborns of mothers with depression symptoms had higher cortisol
levels and lower levels of dopamine and serotonin, two neurotransmitters that have been tied to
depression.
The newborns also had less developed learning skills, they were less responsive to social
stimulation, and they were less able to calm themselves when agitated, said Dr. Tiffany Field, the
author of the study and director of the Touch Research Institutes at the University of Miami
School of Medicine.
In another study, Dr. Monk put newborn babies in specially designed bassinets that were tilted 30
degrees up or down, a standard method of testing a newborn's responsiveness. When a baby's
head is down, the heart rate normally decreases in response to the stress. But newborns with
depressed mothers showed a smaller decrease in heart rate, suggesting that they were less able to
adapt to stress.
What begins in the womb persists into childhood, researchers find. In a study published in 2002
in The British Journal of Psychiatry, researchers asked 7,448 women in England to assess their
level of stress while they were pregnant and answer questionnaires about their children's behavior
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at age 4. The study found that children whose mothers reported high levels of anxiety in late
pregnancy were more likely to have behavior problems - most notably attention difficulties - as 4year-olds.
"Women who scored in the top 15 percent of anxiety had double the risk of having a child with
severe behavioral problems," said Dr. Thomas O'Connor, a professor of psychiatry at the
University of Rochester, who is an author of the study.
The children in the study had a 10 percent chance of having such problems, Dr. O'Connor said,
compared with a 5 percent risk among children in the general population.
Dr. Vivette Glover, a perinatal psychobiologist at Imperial College London and another author of
the study, noted that even though the children of stressed mothers were at increased risk, the rate
of behavior problems remained very low.
"Even with this anxious group of women, 90 percent of children don't have these behavioral
problems," Dr. Glover said. "So even if a woman is pretty anxious, her children are probably
going to be fine."
Screening pregnant women for mental health problems is quite likely to be controversial.
"In terms of public health, it's very important if we could reduce the incidence of behavioral
problems by treating women during pregnancy," Dr. Glover said.
She noted that cognitive behavioral therapy had proven highly successful in treating adults who
suffer severe anxiety.
Some researchers say that any recommendation for screening and treatment during pregnancy is
premature because the research is still preliminary. They point to studies suggesting that a
mother's stress may in some cases be beneficial to her fetus.
In one study, 2-year-olds whose mothers reported high levels of anxiety in pregnancy had better
motor and cognitive skills than children whose mothers did not report being highly anxious.
Some experts say a fetus's awareness that its mother is stressed may serve an evolutionary
purpose, preparing it for entry into a difficult world.
"If a fetus is constantly going to be threatened after he is born, and there's danger to its wellbeing, it may make sense for it to develop a system that produces big responses to stress," said
Dr. Pathik D. Wadhwa, director of the Behavioral Perinatology Research Program at the
University of California, Irvine.
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