OB-GYN 101

Shoulder dystocia means difficulty with delivery of the fetal shoulders.

In a spontaneous vaginal delivery, after the baby’s head passes through the birth canal, the baby’s shoulders normally rotate underneath the pubic bone and then are expelled with the fetal torso and extremities. In a few cases, the shoulder fails to spontaneously pass beneath the pubic symphysis, catching on the pubic bone.

Shoulder dystocia is a dangerous condition because:

1.    If it is not relieved, it can lead to fetal death, and

2.    There is a significant risk of injury to the nerves in the neck from stretching or tearing.

3.    The condition and maneuvers to relieve it are associated with an increased risk of fractures of the clavicle and humerus.

It probably occurs to some degree in between 1% and 5% of all deliveries, depending on the patient population, the experience of the operator, definitional differences, and the accuracy of reporting.

It would likely occur more often, but the maternal pelvis is somewhat stretchy, the fetus is somewhat compressible, most deliveries are of normal size and shaped infants through normal size and shaped pelvises.

Although shoulder dystocia is more common among women with gestational diabetes and those with very large fetuses, it can occur with babies of any size. Unfortunately, it cannot be predicted or prevented, so birth attendants should be prepared to deal with this issue, even if the patient is considered low risk.

Suspect a shoulder dystocia if, after delivery of the head, the fetal head partially withdraws back into the birth canal. This is called the "Turtle Sign". It occurs because the anterior shoulder is stuck behind the pubic symphysis. Insert one finger vaginally, and you will be able to feel the shoulder stuck behind the pubic bone.

In more severe cases, the posterior shoulder may be stuck at the level of the sacral promontory.

You should immediately call for extra help since many of the maneuvers you will need to perform will require more than a single person, anesthesia and newborn resuscitation and support may be needed.

Avoid Excessive Downward Traction
Try to avoid applying excessive downward traction to the baby's head. The nerves of the brachial plexus course through the neck and into the arm. Stretching or tearing of these nerves can cause or aggravate an injury with serious consequences to the baby.

While most of these nerve injuries heal spontaneously and completely, some do not.

Generous Episiotomy
A generous episiotomy can be helpful. If a spontaneous laceration has occurred, or if the perineum is very stretchy and offers no obstruction, then it is not necessary to also perform an episiotomy. However, if there is any soft tissue obstruction or if the perineum interferes with your ability to perform extraction maneuvers, it is wise to place a large episiotomy, a second episiotomy, or extend a perineal laceration with scissors to obtain more room. Some physicians will perform an intentional 4th degree extension in order to facilitate delivery. The 4th degree extension can usually be easily repaired without any long-term consequences for the mother and provides excellent exposure for the delivery.

Gentle downward traction can be attempted initially to try to free the shoulder, although some physicians prefer to not exert any downward traction to facilitate the delivery.

If gentle downward traction has no effect, do not exert increasing pressure. Instead, try some alternative maneuvers to free the shoulder.

McRobert's Maneuver
The McRobert's Maneuver involves flexing the maternal thighs tightly against the mother’s abdomen. This can be done by the woman herself or by assistants.

By performing this maneuver,

1. The axis of the birth canal is straightened, allowing a little more room for the shoulders to slip through, and

2. The pressure of the mother's thighs on her abdomen provides the equivalent of suprapubic pressure to dislodge the shoulder from behind the pubic bone.

With the patient in the McRobert's position, you can try gentle downward traction again. If gentle traction has no effect, stop the traction and try another maneuver.

Suprapubic Pressure
Suprapubic pressure can be applied to drive the fetal shoulder downward, clearing the pubic bone.

It is usually easiest to have an assistant apply this downward pressure while you apply coordinated, gentle downward traction and the mother bears down.

Sometimes, the suprapubic pressure is more effective if applied in a somewhat lateral direction, rather than straight down. This tends to nudge the shoulder into a more oblique orientation, which in general provides more room for the shoulder. Usually, this lateral pressure is directed so as to shove the baby’s shoulder towards its’ breastbone, but any direction of force that is effective in moving the baby’s shoulder away from the entrapped anterior-posterior orientation into a more oblique or lateral orientation can give good results.

Gentle downward traction on the fetal head in combination with this suprapubic pressure, maternal pushing efforts and MacRobert's position may relieve the obstruction. If not, stop the pushing and pulling efforts, and try another maneuver.

Deliver the Posterior Arm
Often, by the time the fetal head has delivered, the posterior arm has entered the hollow of the sacrum. By reaching in posteriorly and sweeping the arm up and out of the birth canal, enough additional space will be freed to allow the anterior shoulder to clear the pubic bone.

Watch a video clip demonstrating this maneuver

This description makes the maneuver sound easier than it is. Because of limited visibility and space, this maneuver is sometimes difficult or impossible.

Identify the posterior shoulder and follow the fetal humerus down to the elbow. Then you can identify the fetal forearm. Grasping the fetal wrist, draw the arm gently across the chest and then out. Once the posterior arm has delivered, you can try each of the previous maneuvers again as you have reduced the bisacromial diameter and it will be easier for the anterior shoulder to descend.

Screw Maneuver
If you try to remove an electric light bulb by simply pulling on it, it won't work. If, however, you unscrew the light bulb, it comes out relatively easily.

The concept of unscrewing the light bulb can be applied to shoulder dystocia problems.

The image shown here shows pushing the anterior shoulder in a counterclockwise direction. As the baby rotates, the posterior shoulder comes up outside of the subpubic arch. At the same time, the stuck anterior shoulder is brought posteriorly into the hollow of the sacrum. As the rotation continues a full 360 degrees, both shoulders are rotated (unscrewed) out of the birth canal.

It is sometimes easier to perform this maneuver with your hand on the posterior shoulder, rotating it up. If you have enough room in the pelvis, using both your hands, one on the posterior shoulder and one on the anterior shoulder can produce excellent results.

In cases where both the anterior and posterior shoulders are stuck, the baby may need to be rotated twice. The first rotation brings a shoulder down into the hollow of the sacrum, while the second rotation brings that shoulder up and outside the subpubic arch.

Shoving Shoulders Saves Scapulas
Two variations on the unscrewing maneuver include:

• Shoving the shoulder towards the fetal chest, which compresses the shoulder-to-shoulder diameter, and

• Shoving the anterior shoulder rather than the posterior shoulder. The anterior shoulder may be easier to reach and simply moving it to an oblique position rather than the straight up and down position may be sufficient

If these maneuvers have failed, it is appropriate to repeat them in various combinations, and with increasing forcefulness. While the increased forcefulness may increase the risk of shoulder injury, the baby must ultimately be delivered or it will die.

There are a few other maneuvers that are infrequently used.

Fundal Pressure
Applying fundal pressure in coordination with other maneuvers may, occasionally, be helpful. Applied alone, it may aggravate the problem and increase the risk of injury by further impacting the shoulder against the symphysis. You also run the risk of uterine rupture if the fundal pressure is applied too vigorously or at the wrong time. For these reasons, many obstetricians recommend avoiding fundal pressure entirely.

Zavenelli Maneuver
Another infrequently-used technique to resolve shoulder dystocia is cephalic replacement of the fetal head, followed by cesarean section. The fetal head is flexed and pushed back up into the birth canal and held in place. The mother is transported to an operating room, and a cesarean section performed. Generally good results have been reported from a small number of cases in which this maneuver has been performed.

Clavicular Fracture
Intentional fracture of the baby’s clavicle has been recommended in the past as a way of narrowing the bisacromial diameter. A fractured clavicle in a newborn usually heals well without long-term consequences and generally poses less of a threat to the newborn than a brachial plexus nerve injury. That said, it is not so easy to intentionally fracture a clavicle. I’ve tried to fracture a clavicle several times during my career, but without success. At the same time, I have inadvertently fractured several clavicles during my 30 years as an obstetrician.

Despite careful attention to detail and skillful performance of these maneuvers, some babies will still sustain injury. No maneuver, no matter how skillfully performed, can prevent all injuries. But the best chance for avoiding injuries comes when shoulder dystocia is approached in a careful, systematic way, with progressive increases in the forcefulness of the maneuvers, until just the right combination of just the right forces delivers the baby.

Revised 1/2009