As soon as shoulder dystocia is identified, the mother's hips are flexed back onto her abdomen. This is called McRobert's Position, and helps the baby's shoulder slip under the mother's pubic bone by enlarging the pelvic outlet. Usually at about the same time, a nurse or other assistant pushes down on the baby's shoulder, behind the pubic bone, helping it pass under. More than half of all shoulder dystocias are relieved just by these two maneuvers, which usually take less than a minute. It is important that the pressure be suprapubic in nature to dislodge the shoulder from beneath the pubic bone and not fundal, or on the top of the uterus, as this serves only to further impact the shoulder beneath the pubic bone.
If the shoulder dystocia persists, direct manipulation of the baby is usually required. If a small incision in the perineum (called episiotomy) hasn't been made yet, it is usually made now to allow enough room for manipulation. There are two basic maneuvers:
- Corkscrew. The shoulders of the baby are twisted around and pushed out of the anterior-posterior (front to back) plane. This may allow the front shoulder to come out from behind the pubic bone and be delivered.
- Delivery of the further arm. The obstetrician reaches back into the birth canal alongside the baby to grasp the baby's further hand or forearm and pull it out by sweeping it across the baby's chest. Once the arm is out, the rest of the baby's body is usually delivered easily. The upper bone of the baby's arm, called the humerus, may be broken during this maneuver, but it heals up quite easily.
It is very rare that the baby cannot be delivered by the maneuvers discussed so far. If the shoulder dystocia persists, however, other rescue maneuvers include:
- Zavanelli Maneuver. The baby's head and body are pushed back into the uterus and cesarean delivery is performed. Although there are some risks to the mother and baby with this procedure, there are many reports of it successfully relieving severe shoulder dystocia. This maneuver would be considered heroic and is not practiced routinely.
- Symphysiotomy. In this procedure, the mother's pubic bone is cut, widening the pelvis and allowing prompt delivery. But since few obstetricians have experience with this procedure, and it can cause injury to the mother's urinary tract, symphysiotomy is not commonly practiced in this country.
- Proctoepisiotomy. In this maneuver, the normal midline episiotomy is extended intentionally into the rectum. Though this requires a complex repair that can lead to future rectal dysfunction, it can also serve to widen the birth canal posteriorly and allow for disimpaction of the anterior shoulder.
Brachial Plexus Injury
Although shoulder dystocia is troublesome, the real risk is a lifelong disability from injury to the brachial plexus?a group of nerves at the base of the neck. This is so rare that it is almost impossible to predict. If every baby thought to be around nine pounds or more were delivered by cesarean, it would take more than 2,500 cesarean deliveries to prevent one permanent brachial plexus injury. Preventing brachial plexus palsy is even more difficult because this injury is not always related to shoulder dystocia. For many years, it was presumed that the baby being pulled too hard at birth caused brachial plexus injury. Now, for the following reasons, it is thought the injury may happen at various other points during labor before the delivery:
- over half the babies born with brachial plexus injuries have no shoulder dystocia;
- ten to 15% of injuries involve the posterior arm;
- 20%of the cases are associated with very rapid labor;
- over half the cases occur in normal-sized babies;
- it is rare with cesarean delivery; and
- it is rare with cesarean delivery; and
- there are rare cases of recurrence within a family.
Predicting Shoulder Dystocia
Recently, many attempts have been made to determine beforehand whether or not a fetus will develop shoulder dystocia. If cesarean delivery could be performed in these cases, shoulder dystocia and brachial plexus injury could be prevented. This idea, while appealing in theory, has proved elusive in practice. There are many factors loosely associated with shoulder dystocia, but not enough for meaningful prediction. Examples of these are the weight of the mother, how much weight the mother gains during pregnancy, and the use of the drug Pitocin to induce labor. Other factors have a stronger association, such as diabetes in the mother, the use of instruments such as forceps or vacuum in delivery, and, most importantly, the baby's weight. Investigators have tried to use these factors to identify which women should have a cesarean section to avoid shoulder dystocia. One of the main problems with these attempts is there are no good techniques for estimating the baby's weight. Even ultrasound has an average of 15% error, and identifies only 60% of all babies who are actually about 9 pounds (over 4 kg). For babies over 9 pounds, the risk of shoulder dystocia is about 10%.