Grantly Dick-Read, an English MD and Obstetrician from the 1920's, discovered there are three layers of the uterine muscle: the outer layer, the middle layer and the inner layer.

When a woman is relaxed and breathing deeply in labour the three uterine muscle layers work together like 'silk on silk' to help the labour progress. This is because a relaxed state promotes the release of higher levels of oxytocin and endorphins. When these circulate freely around the body the uterus receives more blood and can, therefore, work more effectively and efficiently.

Conversely, when a woman breathes quickly through her mouth it creates adrenalin in her system which can make the body tense. This will often create more pain in her body, causing panic and leading her to feel out of control. Grantly Dick-Read called this the Fear-Tension-Pain Syndrome. Adrenaline and stress hormones act on the uterus to divert blood away and cause the inner circular muscle fibres clamp shut. This causes tension within the uterine muscles which stimulates pain receptors that can slow down the labour or even halt it completely.

This is why we always recommend that women breathe in and out the nose as slowly as possible during labour. This supports the body to give birth and also helps the woman feel calm and in control.