What is Shoulder Dystocia?

Shoulder dystocia is a birth complication in which the baby’s shoulders become “stuck” behind the mother’s pubic symphysis on the way down the birth canal. The baby’s head usually does pop out when the mother is fully dilated, but if the physician attempts to use excessive traction on the head to facilitate delivery of the rest of the body, the result can be permanent damage to the brachial plexus.

Shoulder dystocia is sometimes difficult to predict, but it is important for all pregnant women to understand the risks, signs and symptoms in order to avoid injury to the baby. Any concerns should be discussed with your obstetrician, and consent clearly given for a cesarean section delivery if shoulder dystocia does in fact occur.

Risk Factors

In general, the major cause of shoulder dystocia is disproportion of the size of the fetus to the mother’s pelvic opening. Shoulder dystocia can also occur due to positioning of the baby as well. Each of the following risk factors relate to the size or position of the baby.

1. Macrosomia: This means simply a large baby, and is the most common risk factor. The general rule is a baby weighing greater than 4000 grams in a diabetic mother, and greater than 4500 grams in a non-diabetic mother. However, shoulder dystocia is not always reliably predictable based on this factor alone.

2. Pelvic size/shape: An unusually-shaped or small pelvis can complicate delivery, even if the baby is less than 4000 grams. This issue is common in women who are shorter, and should be evaluated early in pregnancy.

3. Maternal diabetes: Diabetes can lead to larger babies, thus increasing risk. Following macrosomia, this is the factor with the closest association with shoulder dystocia. It is important to be tested for diabetes during pregnancy, and if positive, the mother should take every precaution to control her blood sugar in order to reduce the possibility of a larger baby.

4. Maternal obesity: Centers for Disease Control and Prevention defines obesity as a body mass index (BMI) of 30 or higher. A mother who is obese has a high risk of having a larger baby, thus increasing the risk of a difficult delivery due to shoulder dystocia.

5. Excessive weight gain: Excessive weight gain is defined as 30 pounds or more, and can also result in a larger baby and a higher risk of shoulder dystocia. Pregnant mothers should eat healthy and try to limit weight gain during pregnancy to avoid this risk.

6. Women who have had a prior birth with shoulder dystocia are at high risk for complications with subsequent births as well. Pregnant mothers who have this prior history should request a caesarean delivery to avoid this risk.

Signs and Symptoms

Several factors are obvious signs and symptoms of shoulder dystocia, and should raise immediate concern to the obstetrician. Intrapartum factors such as a slow dilation or descent, labor induction, epidural anesthesia, and operative vaginal delivery with forceps and/or vacuum extraction should lead the obstetrician to be alert for the possibility of shoulder dystocia.

The physician should be alerted to the possibility of size disproportion if the dilation and descent is slower than average. This should be carefully evaluated before the use of operative equipment such as forceps or vacuum.

Operative vaginal delivery with the use of forceps and/or vacuum may be used when the baby’s head is delivered, but the rest of the body is larger and cannot be easily delivered through the birth canal. If these maneuvers are required for delivery, the possibility of shoulder dystocia is high.

Multiple attempts at these maneuvers can result in excessive force to the baby, causing permanent injury. The Rule of Threes is a general rule to stop these maneuvers after the third failed attempt. The physician should then reassess and evaluate the possibility of shoulder dystocia as the cause of the difficult delivery, and proceed to cesarean section to safely deliver the baby.

How to Prevent Shoulder Dystocia

There are several other maneuvers the physician can attempt to relieve the shoulder dystocia and safely facilitate a vaginal delivery.

1. McRoberts Maneuver: This is a flexion of the mother’s hips back onto her abdomen, which enlarges the pelvic outlet. This should be performed as soon as shoulder dystocia is suspected. This maneuver, along with pushing the baby’s shoulder to help it pass under the pubic bone, usually relieves the dystocia.

2. Manipulation: The doctor can attempt to manipulate the baby to facilitate relief of the shoulder dystocia in two ways. A Wood’s screw maneuver allows the physician to manually twist the baby’s shoulders to allow the front shoulder to come out from behind the pubic bone. Additionally, the physician can attempt delivery of the baby’s posterior arm by sweeping the arm across the chest and pulling it out, without undue force. This can result in fracture of the baby’s humerus, which usually heals easily, and can save the baby from injury due to the shoulder dystocia.

3. Proctoepisiotomy: The normal episiotomy can be extended into the rectum, which widens the birth canal and can relieve the shoulder dystocia.

4. Intentional fracture of the clavicle: The baby’s clavicle can be purposefully fractured away from the lung, which would disengage the shoulder and relieve the dystocia.

5. Zavanelli Maneuver: This maneuver is a last-resort attempt if the baby cannot be safely delivered by the above measures. The baby’s head and body are pushed back into the uterus and a cesarean section delivery is then performed. This maneuver is considered “heroic” and should not be practiced routinely.

6. Ultimately the occurrence of shoulder dystocia can be avoided best by cesarean section delivery of the baby. If a pregnant mother recognizes any of the above risk factors, signs or symptoms during pregnancy or delivery, a cesarean section should be requested.

Injuries Related to Shoulder Dystocia

The most common injury caused by shoulder dystocia is injury to the brachial plexus, also known as Erbs Palsy. Brachial plexus injuries usually result from negligence and the use of excessive force in attempts to deliver the baby vaginally while trying to relieve the shoulder dystocia. Traction applied to the baby with operative techniques pulls the baby’s head away from the shoulders, which stretches the brachial plexus. If the force is excessive, the nerves can be torn, resulting at times in permanent injury to the nervous system, and can lead to complete loss of muscle control, with loss of feeling in the arm and hand.

There are varying degrees of Erbs Palsy, ranging from damage to the nerve, which usually heals within three months, to complete avulsion, which can result in complete and total loss of function in the limb. Some children experience partial recovery, but have permanent weakness of the shoulder or arm as a result of the injury.

The affected arm is sometimes much smaller than the unaffected arm, a difference that becomes more noticeable as the child gets older. Even with surgery to repair the damaged nerves, most children will not fully recover, and may never have normal function in the arm. Physical and occupational therapy may be helpful in some children to regain minimal function.

Klumpke’s Palsy is a rare form of brachial plexus injury in which injury of the 8th cervical nerve and 1st thoracic nerve result in paralysis of the forearm and hand. Fewer than 50% of affected babies will have spontaneous recovery, with recovery being rarer in those with Horner syndrome, or drooping of the eyelid on the opposite side of the face.

Conclusion

Careful awareness and evaluation of the above risk factors are vital to avoid occurrence of shoulder dystocia and resulting injury. Any negligence or lack of knowledge of the physician can result in lifelong permanent injury to the baby, even with surgery and/or therapy and in-home exercise routines. Therefore, pregnant women should choose their obstetrician or midwife wisely, and give clear consent for a cesarean delivery at the first sign of difficulty due to shoulder dystocia.