An excerpt from Childbirth Without Fear
"Any stress to the mother stimulates the adrenal glands to pour out catecholemines. As a result, muscle sphincters tighten down making uterine contractions less effective and sending blood away from the uterus to the arms and legs because stress and tension prepare the body for fight or flight. All of this prevents an adequate supply of oxygen to the big contracting muscle-the uterus.
There are three muscle layers composing the uterus, the outer muscles contract to push the baby down, through and ultimately out of the uterus.
The middle muscles contract to squeeze the blood out of the walls of the uterus and then relax to allow the blood vessels to fill up again with a fresh supply of blood.
But when the inner circular muscles contract they close the outlet, maintaining the uterus in its unemptied shape. Thus, these inner circular muscles must be loose and relaxed when the long muscles contract to open the womb and push the baby out.
If a woman is frightened during labor this inner muscle layer contracts, then the muscles of the uterus and the muscles that hold it closed are working against each other. Whenever there are two big groups of muscles working against each other they soon begin to hurt and in a short time the pain becomes very severe.
We speak of this as the fear-tension-pain-syndrome of childbirth for a woman who is afraid and unconsciously resisting the birth of her baby by tightening the circular uterine fibers which prevents the progress of the birth and increases muscle tension within the walls of the uterus. This causes nearly all of the pains and distresses in otherwise normal labor. Which describes the labor of about ninety five women out of a hundred."
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