Stress Levels During Pregnancy Affect Fetal Brain Development, Suggests New Study

High levels of stress during pregnancy could result in changes to a baby's amygdala. Image: Subbotina Anna/

A new study in the journal eLife indicates that the degree of stress experienced by pregnant women directly influences the development of their infants’ brains. By analyzing levels of the stress hormone cortisol in new mothers, the study authors were able to highlight a link between this key signaling compound and alterations in the amygdala – a brain region that is heavily involved with emotional processing – of newborns.

In an intriguing and significant twist, though, the researchers noted distinct sex-related differences in these alterations, with certain stress-related amygdala changes occurring in baby boys and others being present in baby girls.

In their study, the authors cite numerous previous papers that found that individuals who are exposed to high levels of stress in the womb tend to have a greater chance of developing mood disorders like depression later in life. However, such studies have generally relied on self-reported questionnaires in order to gauge the amount of stress experienced during pregnancy, rather than analyzing objective biomarkers.

Interestingly, though, one study did find that maternal cortisol levels during early gestation can be used to predict the size of a child’s amygdala at the age of 7. In an attempt to build on this finding, the authors of the new study analyzed hair samples from 78 women who had just given birth, in order to determine their cortisol levels during the final three months of their pregnancy.

The team also used magnetic resonance imaging (MRI) to scan the brains of each woman’s new baby, paying particular attention to the amygdala. An initial look at the results revealed that higher levels of cortisol in a given mother’s hair was linked to structural and functional changes within the amygdala of her baby, indicating that stress during pregnancy directly affects the development of this key brain region.

Upon closer examination, however, the study authors noted that exposure to high cortisol levels in the womb affected babies differently according to their sex. Specifically, maternal stress was found to induce alterations in the actual structure of the amygdala in boys, while in girls it produced changes in the way that the amygdala connects to other parts of the brain.

While the researchers can’t say with any certainty why this is case, they propose that it may have something to do with the fact that the enzymes that control the passage of cortisol across the placenta differ according to the sex of the fetus.

It is also important to note that this study did not look at the emotional development of the babies involved, which means no conclusions can be drawn regarding how these findings might affect personality and mental health later in life.

Regardless, though, the outcomes of this study highlight the importance of minimizing stress during pregnancy. Summing up the gravity of the issue, lead study author James Boardman explained in a statement that “our findings are a call to action to detect and support pregnant women who need extra help during pregnancy as this could be an effective way of promoting healthy brain development in their babies."


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