Stressed babies ‘adjust growth patterns’

According to the scientists,the sex of the baby determines the way it responds to stressors during pregnancy and its ability to survive pregnancy complications — in fact,this sex-specific growth pattern is a result of changes in placental function caused by the stress hormone cortisol.

Professor Clifton said: “What we’ve found is that male and female babies will respond to a stress during pregnancy by adjusting their growth patterns differently. The male,when mum is stressed,pretends it’s not happening and keeps growing,so he can be as big as he possibly can be.

“The female,in response to mum’s stress,will reduce her growth rate a little bit; not too much so she becomes growth restricted,but just dropping a bit below average.

“When there is another complication in the pregnancy — either a different stress or the same one again – the female will continue to grow on that same pathway and do okay but the male baby doesn’t do so well and is at greater risk of pre-term delivery,stopping growing or dying in the uterus.”

Professor Clifton said this sex-specific growth response was observed in pregnancies complicated by asthma,pre-eclampsia and cigarette use but was also likely to occur in other stressful events during pregnancy such as psychological stress.

In female babies,increased cortisol produces changes to the placental function which lead to the reduction in growth,but the increased cortisol levels in a mother carrying a male baby doesn’t produce the same changes in placental function.

This study could lead to sex-specific therapies in pre -term pregnancies and premature newborns,say the scientists.

“We are looking at what events during pregnancy cause changes in how the baby grows,what’s behind this and ways in which we can improve the outcomes for pregnant women and their babies,” she said.