Stage II Of Normal Labour
The second stage of labor starts at the end of the first stage when the cervix is fully dilated to 10 cm. This stage is characterized by some specific dynamics in both the mother and the baby.
In the Mother
Contraction and RetractionPainful, involuntary contractions as well retractions occur in the uterine muscles.
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.
Contraction of the Accessory Muscles:As the second stage starts, the abdominal muscles and the diaphragm, which are the accessory muscles of labor, contract forcefully to expel the fetus. The diaphragm is a tough muscle separating the abdominal cavity from the chest.
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.
Changes in the Surrounding Organs:As the fetus moves into the vagina dilating the vaginal cavity, the structures in front as well as those behind the uterus changes their position. The structures in front - the bladder and the urethra - gets pushed upwards and forwards. This results in ' inability to pass urine' by the woman in labor.
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.
In the Baby 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).
EngagementThe term 'Engagement' is used when the largest diameter of the fetal head is at the level of the smallest diameter of the mother's pelvis. This diameter is between two points on either side of the pelvis known as the ischial spines.
Descent with FlexionThe baby descends deeper into the mother's pelvis. At the same time, the flexion of its body - the arms folded in front of the chest, the legs tucked in front of the abdomen, and the chin touching the chest wall - increases, so that the overall size of the baby becomes smaller and can fit into the pelvis.
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'.
Delivery by ExtensionAs the fetal head reaches the maternal symphysis pubis (the bone just below the mons pubis), it hitches under the bone. The pressure by the uterine contractions causes the neck of the baby to get extended and the baby is born face first. The forehead appears first, then the eyes and nose and lastly the mouth as the neck extends more and more.
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.
Delivery of the ShouldersOnce the head is out, the contractions may or may not decrease in intensity for some time. Then the contractions increase once again, the anterior shoulder (the shoulder just under the symphysis pubis) hitches under the pubic bone and the posterior shoulder (the shoulder towards the rectum) is delivered first.
The body of the baby now slides smoothly out of the vaginal canal.
Steps of Management of the Second Stage of Labour
The principles of management of this stage are (a) to ensure birth of a healthy baby, (b) to prevent damage to the maternal tissues.