By Dr.M.D.Mazumdar, MD
The second stage of labor starts at the end of the first stage when the cervix is about 3-4 cm dilated. This stage is characterized by some specific dynamics in both the mother and the baby.
Retractions mean that the uterine muscles become somewhat shorter after every contraction as the baby descends into the pelvic cavity of the mother. They do not regain their original length even after the contraction is over and the muscles relax.
The contractions of the diaphragm and the abdominal muscles are clinically evident as 'bearing down pains'. The woman in labor takes a deep inspiration and holds her breath, thereby fixing the diaphragm in a lower position, and then contracts the abdominal muscles. This action increases the intra- abdominal pressure, compressing the uterus and helps in increasing the expulsive force.
In the beginning, this secondary power is voluntary and the woman can withhold the urge to push. But in the later part of the second stage, the urge and the pressure becomes involuntary and synchronises with the uterine contractions.
The structures behind the uterus are the rectum, the anus and the perineum (the area between the vagina and the anus). These get displaced downwards and backwards. The result is that the woman gets a desire to pass stool (as a result of pressure upon the rectum), and the perineum becomes stretched and thinned out. The anus opens up as the head descends.
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The baby undertakes a series of movements and changes in position during its passage through the vaginal canal to the vaginal outlet. In a normal labor, the baby faces the mothers back at this time and delivers in this position (with the face towards the mother's back).
When the head of the baby reaches the lowest point of the pelvic floor, it presses against the perineum causing it to bulge slowly. The anus gapes open. The head of the baby is now seen at the vaginal opening. Initially, the head retracts back when the uterine contraction decreases. But later, the head remains at the opening even when there is no uterine contraction. This is called 'Crowning'.
The baby's nose and mouth needs to be suctioned out of any secretions at this time to clear up the respiratory tract and help the baby to breathe properly.
The body of the baby now slides smoothly out of the vaginal canal.
The delivery of the baby signifies the end of the second stage and the beginning of the 'Third Stage of Labor'.
The principles of management of this stage are (a) to ensure birth of a healthy baby, (b) to prevent damage to the maternal tissues.
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