You’d probably guess that stress during pregnancy isn’t going to be good for the baby, but new research reveals that this has different effects on boys and girls – and it may even lead to girls’ IQ scores being higher.
The hormone cortisol, which helps our bodies respond to stress, is thought to be necessary for foetal development. Researchers from the Odense University Hospital in Denmark previously showed that it can advance early language development.
Now, the same team says that too much cortisol during the third trimester of pregnancy (from week 27 to the end of pregnancy, around 37-42 weeks) could impact cognitive function later in life. Specifically, when the child reaches seven years old, they think their mothers' stress during pregnancy may affect the IQs of boys and girls differently.
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Presenting their research at the 26th European Congress of Endocrinology in Stockholm, the researchers say that girls could be less sensitive to cortisol exposure because of the role the placenta plays.
Women carrying girls during pregnancy tend to secrete more cortisol, but an enzyme in the placenta controls how much of it reaches the foetus. This enzyme converts the cortisol into an inactive version of the hormone known as cortisone.
The researchers think that boys may be more vulnerable to cortisol exposure because they don’t have the benefits of this enzyme’s protective activity.
For the new study, the researchers measured the cortisol and cortisone levels in 943 pregnant women. They then compared these to the IQs of their 943 children, measured by trained psychologists seven years later.
They found that boys exposed to higher cortisol levels in the womb had lower IQ scores. But the researchers were surprised to find it was only when cortisol was found in urine samples – rather than in the blood – that girls’ IQs were higher.
“To our knowledge, this is the first study investigating the association between urine cortisone levels during pregnancy and IQ scores in children,” said lead author, Dr Anja Fenger Dreyer.
“While other studies have only looked at cortisol circulating in the blood during pregnancy and child IQ, we are the first to look at urine samples as well as blood samples and to investigate boys and girls separately.”
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