Scientists discover secret to stress-free pregnancy

Previous work has shown exposure to these hormones can increase the risk of children suffering mood disorders such as depression and anxiety in later life.

The discovery of the enzyme by a team at Edinburgh University could lead to new treatments for women subjected to high stress levels during pregnancy, such as through abuse or bereavement. The work is being presented at the Festival of Neuroscience in London today.

Scientists have known for some time that the environment experienced in the womb – where “foetal programming” takes place – can have long-lasting effects on health and cause disease in later life, but how this process works has been unclear.

Professor Megan Holmes, a neuro-endocrinologist at Edinburgh University and the British Heart Foundation Centre for Cardiovascular Science, said the team now believes an enzyme known as 11 beta-HSD2 plays a key role in foetal programming.

The enzyme can be found in the placenta and the foetal brain, where it is thought to act as a shield against stress hormones. Holmes said: “The stress hormone cortisol may be a key factor in programming the foetus, baby or child to be at risk of disease in later life. Cortisol causes reduced growth and modifies tissue development.”

She said the team found that the enzyme was able to break down the stress hormones, making them inactive before they could damage the developing foetus.

The researchers used genetically modified mice, bred to lack this particular enzyme. Holmes said: “In mice lacking the enzyme, foetuses were exposed to high levels of stress hormones and, as a consequence, these mice exhibited reduced foetal growth and went on to show mood disorders in later life.

“We also found that the placentas from these mice were smaller and did not transport nutrients efficiently to the developing foetus.”

The scientist said determining the exact mechanisms involved in foetal programming would help identify “potential therapeutic targets” to reverse the consequences of offspring suffering mood disorders.

She said there was a “natural variation” of the enzyme in humans, meaning some women may have lower levels which increased the risk of harmful effects to their children if they were exposed to extreme stress.

Once scientists know exactly how the enzyme protects the foetus, these women could have treatment to avoid harmful effects on babies.

But Holmes said that this would probably be targeted at women suffering extremely stressful situations, where the baby was at highest risk.

“Most of the stresses that are used in this research are long and chronic,” she said.

Twitter: @LyndsayBuckland