澳门金沙游戏网页版:Bumpology: How does stress affect my fetus?
By Linda Geddes Days till birth: 146 Waist circumference: 77.5 centimetres (30.5 inches) Five months to go until I give birth to our first child, and the trials of life and work are starting to get to me. If that weren’t enough, the onslaught of news stories about stress during pregnancy is enough to raise my blood pressure still further. Last week it was stress during pregnancy gives your child asthma. Then there were the studies hinting that stress inhibits growth in the emotional areas of babies’ brains, raises the risk of stillbirth and makes your child more likely to develop schizophrenia. What’s a pregnant woman to make of all this? One of the problems with these studies is that repeatedly stressing animals in a lab environment is hardly the same as juggling work deadlines, gym classes and social arrangements. Neither is London, my home, a war zone – as was the location in the schizophrenia study. What we need are studies that measure stress more directly, and fortunately I’ve found two that do just that. Unlike many previous studies, they rely on direct measurements of the fetus or its immediate environment, the amniotic fluid. And they are throwing up some surprising results, including that moderate levels of stress might be good for fetal development. In the first study, Janet DiPietro and her colleagues at Johns Hopkins University in Baltimore, Maryland, examined 112 healthy pregnant women living in the US three times during their third trimester. They asked the women about their stress levels and recorded fetal movements. They also examined the babies two weeks after birth. The fetuses of women who reported higher stress levels during pregnancy moved around more in the womb. After birth, these babies scored higher on a brain maturation test, although they were more irritable. The more active fetuses also had better control of body movements after birth. Perhaps, says DiPietro, because they were practicing or exercising in the womb. Since the stress hormone cortisol is known to play a role in normal brain maturation, it’s possible that moderate, short-lived stress in mothers-to-be might accelerate this process and actually be good for fetuses – although it is unknown if there is any long-term advantage. But fetuses also make their own cortisol, and it’s unclear from this study whether the positive effects of stress are being mediated through maternal transfer of cortisol or whether the fetus is responding to other changes in the mother’s body, such as heart rate or blood flow. The picture gets more complicated with the second study, in which cortisol was measured in a sample of amniotic fluid. Until now, it has been difficult to test just how much of this hormone human fetuses are typically exposed to. Vivette Glover of Imperial College London and her colleagues analysed amniotic fluid from 125 women who were already undergoing amniocentesis, in which a small sample of fluid is removed from the womb in order to check for birth defects. Potentially in contrast to DiPietro’s study, Glover’s team found that women with high cortisol went on to have children who showed poorer mental and physical development at 18 months of age. However, this was only true in children who failed to form a close bond with their mother, as assessed by a standard test of mother-baby attachment. Glover’s interpretation is that striving to form a close bond with your baby during the early months of life compensates for the negative effects of excess cortisol. “Sensitive mothering can have quite a buffering effect,” she says. To go back to my question, though, what’s a pregnant woman to do? First, it seems that how stressed you say you feel bears little relation to the amount of cortisol in the womb. And second, neither of these studies alters the conclusion that very high stress levels are damaging. Given that my stress levels likely fall into the moderate category, I’m going to be following DiPietro’s advice: “Relaxation is good during pregnancy – if you like to relax. But there is no evidence that everyday stress has any adverse effects on [your baby’s] development.” Journal references: Child Development, DOI: 10.1111/j.1467-8624.2009.01384.x; Biological Psychiatry, DOI: 10.1016/j.biopsych.2010.01.002 More on these topics: