High levels of stress during third trimester of pregnancy linked to lower IQ in male children, study finds

Being stressed during the third trimester of pregnancy could lead to a lower IQ in male children, according to a new study.

When women are pregnant their levels of cortisol – a steroid hormone that is released in response to stress – naturally rise.

It is required for the healthy development of a baby and has a positive influence on the development of their brains.

However, researchers have found that excessive levels of the hormone during the last three months of pregnancy may impede IQ scores in boys aged seven years old.

To examine its effect on cognitive function in children as they grow up, researchers analysed data on the cortisol levels of 943 pregnant women during their third trimester and the IQ tests of their children at the age of seven.

They discovered pregnant women carrying a boy had lower cortisol levels circulating in the blood than those carrying a girl.

However, boys exposed to higher cortisol levels in the womb scored lower on IQ tests at the age of seven.

Girls, on the other hand, did not seem to be affected.

The researchers, from Odense University in Denmark, said their findings suggest boys may be ‘more vulnerable to prenatal exposure’ of cortisol compared to girls.

A previous study, carried out by the same research team, found that children between the ages of one and three have more advanced speech and language skills when their mothers have high levels of cortisol during their third trimester.

That study found that boys whose mothers were exposed to high levels of stress could say more words at ages 12-37 months, while girls were better at understanding more words at the age of 12-21 months. 

Researchers found that children whose mothers had experienced high levels of stress tended to display lower IQ by the age of seven (file photo 

Lead author Dr Anja Fenger Dreyer said: ‘Although our previous study showed prenatal cortisol exposure was positively associated with language development, in this study prenatal cortisol exposure is negatively associated with IQ scores.

‘This may mean that the high levels of prenatal 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.’

Separate research has also found that babies exposed to high levels of cortisol are more likely to develop behaviour problems and stress-related diseases later in life.

Meanwhile, experts have previously suggested that women who are stressed at the time of conception are twice as likely to have a girl.

The findings were presented at the European Congress of Endocrinology in Stockholm.