Stress experienced by a woman during pregnancy may have an effect on her unborn child, most likely mediated by the transfer of stress hormones across the placenta. Research published in May's edition of Clinical Endocrinology shows that from 17 weeks, the amount of stress hormone in the amniotic fluid surrounding the fetus is positively related to that in the mother's blood. This is the first report of this relationship noted at such an early stage in pregnancy.
Stress hormones are pumped into our blood when we become anxious. These hormones are good in the short term because they help our bodies deal with the present stressful situation. But if we are stressed for a long time they can affect our health including making us tired, depressed and more prone to illness. Although we know stress during pregnancy affects the unborn child, little is understood about the mechanisms behind this or when in development the child is most susceptible to these effects.
Researchers led by Prof Vivette Glover at Imperial College London and Dr. Pampa Sarkar at Wexham Park Hospital Berkshire examined the relationship between the stress hormones in the mother's blood and stress hormones present in the amniotic fluid around the baby in the womb. They studied 267 women, taking a blood sample from the mother and a sample from the amniotic fluid surrounding the baby. They then measured the levels of the stress hormone cortisol in both samples. At gestational age of 17 weeks or greater they found that the higher the cortisol levels in the mother's blood, the greater was the level of cortisol in the amniotic fluid. Amniotic fluid is predominantly produced by the fetus, and reflects the exposure of the fetus to various substances including hormones.
Recent work on animals shows that high levels of stress in the mother during pregnancy can affect brain function and behavior in her offspring. While evidence in the scientific literature suggests that maternal stress in humans can affect the developing child, the mechanisms and period of time when the fetus is susceptible is still unclear. This is the first study to show that maternal stress may affect the unborn child as early as 17 weeks in development. More work is now needed to better understand the mechanisms of this relationship and the implications to the unborn child.
Commenting on the study lead author Dr. Pampa Sarkar said: "We are all a product of our developmental history. One of the times when we are most susceptible to the influences of our surrounding environment is when we are developing as a fetus in our mother's womb. Our research shows that the fetus is exposed to cortisol in the maternal blood, and we also demonstrated that at and above 17 weeks, the cortisol in amniotic fluid had a strong positive relationship with cortisol in maternal blood. We found that the strength of this correlation became stronger with increasing gestational age.
"We now need to carry out further work to unravel the mechanisms by which maternal stress affects the fetus, both during fetal life and through into childhood. We do not wish to unduly worry pregnant women. It should be remembered that one of the best ways for people to avoid general stress is to lead a healthy, balanced lifestyle."
Sarkar P, Bergman K, Fisk NM, O'Connor TG, Glover V.
Ontogeny of foetal exposure to maternal cortisol using midtrimester amniotic fluid as a biomarker.
Clin Endocrinol (Oxf). 2007 May;66(5):636-640. [Abstract]