Birth: the birth of baby
The birth or parturition is all mechanical and physiological phenomena that lead to the birth of the child and the expulsion of its Annexes to the outside of the uterus. The first part is the work, the second is the issue.
The work begins with contractions.
For the mother and father who are prepared, this is the big time, as expected.
In the delivery room, the work is monitored by regular clinical assessment and monitoring. Examination of the fetal heart rate (FCR) enables the detection of fetal suffering. The mother is placed on a drip.
Childbirth: workflow
It takes place in two phases. The first is the effacement and dilation of the cervix. The second is the output of the baby or expulsion.
How the work goes off there?
It is a multifactorial set in which all aspects are not fully known.
Hormones are the front line with oxytocin and prostaglandins. But probably also due to mechanical factors increasing the size of the uterus that causes the stretching of its walls and triggers contractions.
In late pregnancy, estrogen is the highest level in maternal blood, while progesterone remains constant or decreases slightly.
These high levels of estrogen stimulate the synthesis of oxytocin receptors on the plasma membrane of myometrial cells (the lining of the uterus consists of endometrium, myometrium) but also oppose the 'muscle-relaxing effect of progesterone. The myometrium gradually becomes more excitable, while weakening, causing low myometrial contractions called Braxton-Hicks. These are the source of false labor.
The role of hormones in birth
But under the influence of oxytocin produced by the pituitary gland of the fetus, the placenta secretes prostaglandins. These two hormones stimulate powerfully the myometrium. Prostaglandins play a role in the synchronization of myometrial contractions. The myometrium made very sensitive to oxytocin, contractions intensify.
At the same time, under the effect of physical and emotional stress felt by the mother, the maternal hypothalamus sends a signal to the maternal neurohypophysis it releases oxytocin.
Oxytocin and prostaglandins are now at high concentrations will trigger rhythmic contractions of true labor.
A mechanism is set up when the hypothalamus came into action. It involves the mechanoreceptors of the uterus. Strongly stimulated, they allow an increased secretion of oxytocin by the hypothalamus, causing stronger contractions.
Moreover, a change of state of fetal fibronectin (a glycoprotein that links maternal and fetal tissue) just before the onset of labor contractions also promotes real work.