Mom’s Stress During Pregnancy May Influence Child’s IQ: Study

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A mother’s stress levels during pregnancy can directly influence her child’s IQ, but the precise impact of stress depends on the child’s gender, new research suggests.

Elevated cortisol levels in the third trimester are linked to lower IQ scores in 7-year-old boys, while higher urine cortisone levels during pregnancy were associated with higher IQ scores in girls.

The study, which was showcased at the 26th European Congress of Endocrinology in Stockholm, shed light on the role of a specific placental enzyme, 11β-HSD2, in modulating fetal exposure to cortisol. This enzyme facilitates the conversion of the stress hormone cortisol into its inert form, cortisone, thereby controlling the levels of cortisol that reach the developing fetus.

Maternal Stress Hormones Affect Child IQ Differently

“We are the first to look at urine samples as well as blood samples and to investigate boys and girls separately,” Dr. Anja Fenger Dreyer, who holds a doctorate in endocrinology and is the lead researcher, said in a press release.

The research team, from Odense University Hospital in Denmark, analyzed data on cortisol and cortisone levels of 943 pregnant women during their third trimester. They also analyzed IQ tests of their children at age 7.

Pregnant women carrying male fetuses had lower circulating cortisol levels in their blood compared to those carrying female fetuses, according to the results.

Boys exposed to higher levels of cortisol in the womb scored lower on IQ tests at age 7. Conversely, girls scored higher on IQ tests when their mothers had higher levels of urine cortisone during pregnancy.

“Our results show that girls may be more protected by the activity of placental 11β-HSD2, whereas boys may be more vulnerable to prenatal exposure of maternal physiological cortisol,” Ms. Fenger Dreyer said.

The study indicates that the 11β-HSD2 enzyme’s activity more effectively shields female fetuses from the potential negative impacts of excess maternal stress hormones, she noted.

A Dichotomy of Effects

Cortisol is a steroid hormone produced by the adrenal glands located at the top of the kidneys. When the body is under stress, cortisol is released to help regulate the body’s response.

Also called “the stress hormone,” it works by releasing glucose from the liver to maintain energy levels during stressful periods. Cortisol also helps regulate metabolism, blood pressure, and suppress inflammation. However, prolonged stress can subject the body to constant cortisol exposure, which can lead to health problems, including hypertension and memory problems.

For developing children, exposure to stress hormones has also been found to affect cognitive and language development.

Ms. Fenger Dreyer and her research team previously studied the effects of stress hormones on developing fetuses. They found that children between the ages of 1 and 3 had more advanced speech and language skills when their mothers had higher levels of cortisol in their blood during the third trimester of pregnancy, according to the results published in the Journal of Neuroendocrinology.

“Although our previous study showed prenatal cortisol exposure was positively associated with language development, in this study prenatal cortisol exposure — ‘directly’ by serum cortisol and ‘indirectly’ by urine cortisone — is negatively associated with IQ scores,” Ms. Fenger Dreyer said.

High prenatal exposure to cortisol could have only a temporary effect on a child’s cognitive development.

It is important to note, according to Ms. Fenger Dreyer, that the data on toddlers’ vocabulary skills in the previous study was based on parent reports, whereas the IQ scores of the children in the current study were evaluated by trained professionals using standardized assessments.