High levels of stress during the late stages of pregnancy may impair IQ scores in young boys, a new study suggests.
Researchers at Odense University Hospital in Denmark found that increased cortisol, a stress hormone, in the third trimester may have a lasting impact on boys aged seven, but not girls.
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The findings highlight the important role cortisol plays in the in utero development of boys and girls independently.
Cortisol is a steroid hormone that helps the body respond to stress and is essential for fetal development. It is also thought to affect cognitive function in children later in life. During pregnancy, the levels of cortisol increase and pregnant women carrying girls generally secrete more cortisol than those with boys.
Cortisone is an inactive form of cortisol. In the placenta, an enzyme called 11β-hydroxysteroid-dehydrogenase type 2 (11β-HSD2) regulates the amount of cortisol that reaches the fetus by converting cortisol to cortisone.
For the study, the researchers analyzed data on the cortisol and cortisone levels of 943 pregnant women during the third trimester. Their children then underwent IQ tests when they reached the age of seven.
The results of the study showed that boys exposed to higher cortisol levels in the womb scored lower on IQ tests at age seven. Additionally, girls the same age scored better on IQ tests when their mothers had higher levels of cortisone in their urine.
In other words, boys appear to be less "protected" by the enzyme 11β-HSD2—and therefore may be exposed to more cortisol.
Lead author, Dr. Anja Fenger Dreyer, said in a statement: "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."
"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," added Fenger Dreyer.
"This may mean that the high levels of prenatal cortisol exposure might have a temporary effect on a child's cognitive development. It should also be noted that the vocabulary in toddlers was reported by parents in our previous study, while child IQ in this study was assessed by trained psychologists."
The full findings of the study were presented at the 26th European Congress of Endocrinology in Stockholm.
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