stress hormones: why are they so important in pregnancy?

Have you ever wondered why your sleep is disrupted in pregnancy? Why do you think you wake up so many times during the night, and, especially in the last month, why do you wake up at 4 a.m. and find that you cannot go back to sleep? It's not ONLY because of needing to go to the toilet but also because of stress hormones!

The stress hormone CORTISOL is the enemy of sleep. When you are not pregnant it is produced in a surge in the morning when you wake up and then is at its lowest level at night when you want to sleep. Unfortunately all pregnant women have cortisol in abundant quantities, not because they are (necessarily) stressed but because their adrenal glands are producing it in increasing amounts throughout pregnancy. Why is this? That's not entirely understood but there are some theories.

1. labour is stressful and painful and perhaps we (Mum and baby) need this vast surplus of stress hormones to vaguely cope with the process of giving birth.

2. cortisol is an immunosuppressant so perhaps we need it so that our bodies will not 'reject' the 'foreign invader'!

3. fetuses need cortisol in order to mature their organs enough to be able to live outside the womb; since mother's cortisol crosses the placenta this helps for baby to get ready to come out.

4. cortisol helps a body to retain water....that's something anyone who has been or is pregnant knows very well - pregnancy swelling, especially in the last month. It is necessary, though, because your body anticipates losing a lot of blood in the process of giving birth so it take out some insurance.

In truth the body's stress hormones play a much more complex role in pregnancy than most people realise. The two brain hormones that cause cortisol to be released by the adrenals (glands above the kidneys) are called CRH and ACTH for short. These are the brain hormones that are released when a body perceives that it is stressed, either physically or mentally. Strangely, the brain hormone CRH is produced by the PLACENTA in pregnancy. That placental CRH is identical to brain CRH in all but one way - there seems to be no 'off switch' for it and the placenta keeps on producing more and more as pregnancy goes on. Very high levels of this hormone towards the end of pregnancy seems to trigger labour, although scientists are not yet sure exactly how. Because CRH ultimately triggers the release of cortisol, more CRH means more cortisol and, indeed, this is WHY we end up having all that cortisol on board.

All this happens NORMALLY in pregnancy not only if you are stressed out or depressed. But researchers hypothesize that stressed and depressed women might have some kind of OVERactivation of this stress system, causing higher levels of CRH and cortisol earlier in pregnancy; this might be the reason that women with pregnancy depression tend to deliver earlier.

There is evidence to suggest that the body's stress hormone system is activated in depressive illness. Click here to read research findings about stress hormones and depression.