Children whose mothers experienced prolonged periods of stress during pregnancy are at greater risk of developing a mental or physical illness later in life, such as attention-deficit hyperactivity disorder (ADHD) or cardiovascular disease.
Now a new study by researchers at the University of Zurich in Switzerland helps uncover the mechanisms behind this risk. Their findings show that long-term physical stress to the mother can change the metabolism in the placenta and influence the growth of the unborn child. Short-term stress, however, does not seem to have a negative effect on the development of the fetus.
During difficult situations, the human body releases hormones to handle the greater stress. This includes the corticotropin-releasing hormone (CRH), which leads to an increase in the stress hormone cortisol — a mechanism which also persists during pregnancy. Furthermore, the placenta, which supplies the fetus with nutrients, can also emit stress hormone CRH.
As a result, a small amount of this hormone enters the amniotic fluid and fetal metabolism. Previous studies on animals have shown that this hormone can boost the development of the unborn baby. Unfavorable conditions in the mother’s environment, for example, can lead to an increased release of the hormone, thereby improving the chances of survival in case of a premature birth.
Under prolonged circumstances, however, this increase can also have negative consequences. “An excessive acceleration of growth may occur at the expense of the proper maturation of the organs,” said Dr.Ulrike Ehlert, psychologist and program coordinator.
To test whether short-term stress affects the fetus, the researchers evaluated 34 healthy pregnant women, who were getting an amniocentesis within the scope of prenatal diagnostics. This procedure is comparable to a short-term stressful situation as the expectant mother’s body briefly secretes cortisol during the test.
To determine whether the placenta also releases stress hormones, the researchers compared the cortisol level in the mother’s saliva with the CRH level in the amniotic fluid and determined that there was no connection. “The baby obviously remains protected against negative effects in case of acute, short-term stress to the mother,” Ehlert said.
The situation regarding prolonged stress is completely different, as was determined using questionnaires for diagnosing chronic social overload.
“If the mother is stressed for a longer period of time, the CRH level in the amniotic fluid increases,” said Dr. Pearl La Marca-Ghaemmaghami, psychologist and program researcher.
This higher concentration of stress hormone in turn accelerates fetal growth. This has been observed in animals such as tadpoles. If their pond is on the verge of drying out, for example, CRH is released in tadpoles, thereby driving their metamorphosis.
“The corticotropin-releasing hormone CRH obviously plays a complex and dynamic role in the development of the human fetus, which needs to be better understood,” said La Marca-Ghaemmaghami.
In conclusion, the researchers suggested that pregnant women exposed to longer-term stressful situations may want to seek support in order to help reduce stress levels. Stress during pregnancy cannot always be avoided, however.
But, said La Marca-Ghaemmaghami, “A secure bond between the mother and child after the birth can neutralize negative effects of stress during pregnancy.”
Source: University of Zurich