Shoulder dystocia: Clinical sciences

Shoulder dystocia is an unpredictable obstetric emergency! It most often occurs during a vaginal delivery when the anterior fetal shoulder becomes impacted behind the maternal symphysis pubis, thereby preventing spontaneous delivery of the fetal body after delivery of the head.

Less frequently, it may occur if the posterior shoulder becomes impacted by the sacral promontory. Once diagnosed, time is of the essence, as the longer a fetus remains impacted, the higher the risk of maternal and fetal morbidity.

Okay, when a patient presents with a chief concern suggesting shoulder dystocia, you should first obtain a focused history and physical exam. The patient may have a history of prior shoulder dystocia, a pregnancy complicated by suspected fetal macrosomia, or they may have gestational or pregestational diabetes. While these findings are associated with an increased risk of shoulder dystocia, it most often occurs in non-diabetic patients with normal-sized infants.

Additional risk factors that may increase the risk of shoulder dystocia include maternal obesity, as this is associated with maternal diabetes and fetal macrosomia; post term pregnancies, or those lasting beyond 42 weeks; an abnormal pelvic structure; or a short maternal stature. Also, a prolonged second stage of labor should raise suspicion, although this alone is not a good predictor for shoulder dystocia.

When it comes to the physical exam, you might see the delivered fetal head retracting against the perineum, which is called the “turtle sign.” Additionally, the fetal shoulders will not easily deliver despite gentle downward traction of the fetal head. Basically, if you see a fetal head that delivers without spontaneous delivery of the body, you can diagnose shoulder dystocia.

Here’s a high-yield fact! Be sure to avoid forceful traction on the fetal head, as it may cause a brachial plexus injury! Erb’s palsy, or injury to C5 through C7 causes the classic “waiter's tip” posture; whereas Klumpke’s paralysis, or injury to C8 through T1 results in a “claw hand” appearance of the infant’s extremity. Generally, brachial plexus injuries are not permanent, and most resolve by 24 months.

Okay, let’s move on to acute management. Remember, shoulder dystocia is an obstetric emergency, so your first step is to immediately call for help! This includes additional nurses, another obstetric care provider, anesthesia, and the neonatology team.

Next, instruct the patient to stop pushing, as further expulsive efforts may worsen the impaction of the shoulder. Also, start a timer and assign one person to record the events. The recorder will note how long the dystocia lasts, as well as when a maneuver is started and for how long it is attempted. Following this, you should evaluate the need for an episiotomy, which is a procedure that enlarges the vaginal opening by making a small incision at the introitus. In this scenario, an episiotomy may provide additional space for you to better perform the maneuvers needed to deliver the fetus.

Speaking of maneuvers, the goal of these is to dislodge the impacted shoulder and allow for delivery by creating a larger space in the bony pelvis; by decreasing the fetal bisacromial diameter, which is the distance between the outermost parts of the fetal shoulders; or by altering how the bisacromial diameter is situated within the bony pelvis.

First-line interventions consist of external maneuvers, specifically the McRoberts maneuver and suprapubic pressure. These are both easy and quick to perform and often are initiated together. The McRoberts maneuver involves hyperflexion of the maternal hips, or flexing the maternal knees and bringing them to her chest. This straightens the maternal sacrum and lumbar spine, thereby increasing the anterior-posterior diameter of the pelvis, which may dislodge the dystocia.

McRoberts should be performed by two assistants, while another assistant uses the heel of their hand to apply suprapubic pressure in a downward and lateral motion on the posterior aspect of the fetal impacted shoulder. The aim is to adduct the fetal shoulder thereby decreasing the fetal bisacromial diameter. Once completed, assess the response of these two maneuvers.

If there is an adequate response you will be able to deliver the neonate with gentle downward traction on the fetal head. However, if the response is inadequate you will note a persistent dystocia and must proceed with additional maneuvers.