By listening intently to movements and heartbeats, researchers are finding that the foetuses 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 behavioural 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 behavioural 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 foetus have been well documented in animal studies. In rats, researchers have found, babies born to stressed mothers show permanent changes in brain chemistry and behaviour. 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 foetuses 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.

Monk has looked at the increase and decrease in a foetus? heart rate when its mother is under stress. 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 foetuses were more varied. The foetuses of mothers who were depressed or had anxious personality styles showed increases in heart rates. In contrast, the heart rates of foetuses whose mothers were emotionally healthy showed no fluctuations.

Monk said the foetuses were not simply mimicking their mothers? responses. ?What this leaves us with is another interpretation,? she said. ?The foetuses of depressed or highly anxious women are more reactive to stimuli than other foetuses.? She compared the foetuses? responses to the way people in a waiting room might react differently to a door being slammed. In this case, a foetus might be reacting to the mother?s increased heartbeat or breathing, or to a jolt of stress hormones.

Early sign: Newborns with stressed mothers can’t adapt to stress

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 foetus 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,? Monk said. ?This may make foetuses 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 DiPietro, pregnant women who perceived their lives, and in particular their pregnancies, as stressful, had foetuses who were more active in an ultrasound test.

Other studies have linked higher levels of stress hormones in the mother with a more active foetus. DiPietro has found that more active foetuses tend to become more active one-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, 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.