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

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.

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. 


Professor Rebecca Reynolds, Laura Stirrat, Professor Jane Norman

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

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