I am more and more convinced that the participation of the father is one of the main reasons for long and difficult labours.

First, a labouring woman needs to be protected against any stimulation of the thinking part of her brain - the neocortex - for labour to proceed with any degree of ease.

This part of the brain needs to take a back seat and allow the primal "unthinking" part of the brain connected to basic vital functions to take over.

A woman in labour needs to be in a private world where she doesn't have to think or talk.

The second reason is that the father's release of the stress hormone adrenaline as he watches his partner labour causes her anxiety, and prevents her from relaxing.

No matter how much he tries to smile and appear relaxed, he cannot help but feel anxious. And the release of adrenaline is contagious.