Stress and obesity in pregnancy: do stress hormones increase the risk of complications?

Professor Rebecca Reynolds, Laura Stirrat, Professor Jane Norman

Cortisol, the stress hormone, may be linked to pregnancy complications such as growth restriction and babies born heavier than normal.

In previous work supported by Tommy's, researchers showed that levels of stress hormones were lower in obese pregnant women compared with pregnant women of normal weight. We are now looking at why this is the case, and if these changes in stress hormones might contribute to pregnancy complications.

This study looks in particular at the “pulsatile release of cortisol” (the PIPa study). Cortisol is a hormone that is normally released in response to stress. During pregnancy, levels of cortisol increase. It is normally at a high level in the morning and a low level in the evening, and is released into the body from the adrenal gland in pulses about once every hour.

Scientists measured the cortisol levels in obese, non-obese, pregnant and non-pregnant women. From this, they were able to show that during pregnancy, the level of cortisol, the frequency of pulses, and how much cortisol was released during each pulse all increased. The further into the pregnancy, the more these measures increased.

These results suggest that during non-obese pregnancy, the higher cortisol pulses may be related to pregnancy complications, including both growth restriction and larger than normal babies (these babies are Large for Gestational Age, or LGA). We are continuing work on how and why these pulses change in obese pregnancy. If we can show that these pulses are also linked to pregnancy complications in obese women, then we may be able to improve a baby’s chances by monitoring women at risk and intervening if necessary.

Our researchers have also looked at the way cortisol is processed by the placenta. They found that the placenta acts as a major ‘barrier’ to cortisol. This protects the baby from too much cortisol as well as from the changes in stress hormones that occur around the time of labour. 

Further studies are now needed to understand the process of mother-to-baby cortisol transfer.

Dr Laura Stirrat was awarded a prestigious Presidential Prize for her work on cortisol levels.

One of the researchers on this project, Dr Laura Stirrat, was awarded a Presidential Prize at the International Society for Reproductive Investigation 2015 for her work on cortisol levels in obese pregnancy. 

Thanks for your interest in our research

Tommy's funds research across the UK investigating the reasons for pregnancy complications and loss. Maternal and fetal research is underfunded and we need your support to continue. There are many small and large ways you can support us, find out more here.


This study is fully funded by Tommy's and takes place in a Tommy's centre

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