A new study has found that stress during the later stages of pregnancy can lower the intelligence levels of boys before they are even born. Researchers discovered that higher levels of the stress hormone cortisol during the third trimester can negatively impact the IQ scores of boys by age seven. However, cortisol levels in the blood were not associated with IQ scores in girls. In fact, higher urine cortisone levels in girls actually improved their scores according to the study.
The Danish research team highlighted the important role that cortisol plays in fetal development for both boys and girls. Prenatal exposure to cortisol, a steroid hormone that helps the body respond to stress, is crucial for the development of the fetus and is believed to affect brain function later in life. The levels of cortisol increase during pregnancy, and women carrying girls typically secrete more cortisol than those carrying boys. However, an enzyme in the placenta called 11beta-HSD2 regulates the amount of cortisol reaching the fetus by converting it to an inactive form known as cortisone.
Previous research by the Danish team had shown that children ages one to three had more advanced speech and language skills when their mothers had high levels of cortisol during the third trimester. For the current study, data on cortisol and cortisone levels of 943 pregnant women during the third trimester were analyzed along with the IQ tests of their 943 children at age seven. The results showed that pregnant women carrying boys had lower cortisol levels in their blood compared to women carrying girls. Boys exposed to higher levels of cortisol in the womb scored lower on IQ tests at age seven, while girls scored better when their mothers had higher levels of urine cortisone.
Dr. Anja Fenger Dreyer, the lead author of the study, noted that this research is the first to investigate the association between urine cortisone levels during pregnancy and IQ scores in children. While previous studies had focused on cortisol circulating in the blood during pregnancy and child IQ, this study examined urine samples as well as blood samples and analyzed boys and girls separately. The findings suggest that girls may be more protected by the activity of placental 11beta-HSD2, while boys may be more vulnerable to prenatal exposure to maternal cortisol. The high levels of prenatal cortisol exposure may have a temporary effect on a child’s cognitive development according to the research.
The study findings are being presented at the European Congress of Endocrinology, where Dr. Fenger Dreyer emphasized that while a previous study had shown a positive association between prenatal cortisol exposure and language development, this study found a negative association between prenatal cortisol exposure and IQ scores. The researcher also noted that the vocabulary in toddlers was reported by parents in the previous study, while child IQ was assessed by trained psychologists in this study. The research sheds light on the potential impact of stress and cortisol levels during pregnancy on the cognitive development of children, particularly highlighting the differences between boys and girls in response to prenatal cortisol exposure.
