Shoulder dystocia is a birth complication that, while concerning for expectant parents, is generally rare and often manageable. It is a situation that requires prompt and skilled action from the medical team during labor and delivery. Understanding this event, its frequency, and how it is addressed can help alleviate some anxieties for those preparing for childbirth.
What is Shoulder Dystocia?
Shoulder dystocia occurs when, after a baby’s head has been delivered during vaginal birth, one of their shoulders becomes lodged behind the mother’s pubic bone. This obstruction prevents the rest of the baby’s body from emerging without additional intervention. It is considered an obstetric emergency due to the potential for complications if not resolved quickly.
A key sign of shoulder dystocia is often referred to as the “turtle sign,” where the baby’s head retracts slightly back into the vagina, similar to a turtle pulling into its shell. This indicates the baby’s shoulders are not advancing through the birth canal. Delays in resolving shoulder dystocia can impact the baby’s oxygen supply.
How Often Does Shoulder Dystocia Occur?
Shoulder dystocia is an infrequent event in vaginal births. Reported incidence rates generally range from approximately 0.2% to 3% of all vaginal deliveries.
The frequency of shoulder dystocia can vary depending on factors like the baby’s birth weight. For larger babies weighing over 8 pounds, 13 ounces, the incidence can increase to 5% to 9%. However, more than half of shoulder dystocia cases occur in babies with a normal birth weight, making it largely unpredictable.
Factors That Increase Likelihood
Several factors can increase the statistical probability of shoulder dystocia occurring, though its onset is often unpredictable. One significant factor is fetal macrosomia, which refers to a baby weighing more than 8 pounds, 13 ounces (4000 grams) at birth. Larger babies present a mechanical challenge due to their size relative to the maternal pelvis.
Maternal diabetes, including both pre-existing and gestational diabetes, also increases the likelihood. Babies of diabetic mothers may have disproportionately larger shoulders and more body fat, which can contribute to impaction. Maternal obesity and excessive weight gain during pregnancy are additional risk factors, as they can also lead to larger babies.
A history of shoulder dystocia in a previous pregnancy also elevates the risk for future deliveries. Certain labor and delivery characteristics, such as a prolonged labor or the use of assisted vaginal delivery (like forceps or vacuum extraction), have also been associated with a higher chance of shoulder dystocia.
Resolution During Delivery
When shoulder dystocia occurs, medical professionals are trained to act quickly and systematically to free the baby. The initial and most commonly used approach is the McRoberts maneuver. This involves hyperflexing the mother’s legs up towards her abdomen, which helps to rotate the pelvis and widen the pelvic outlet. This maneuver alone is successful in a significant number of cases.
Often, McRoberts maneuver is combined with suprapubic pressure. This involves an assistant applying firm pressure to the mother’s lower abdomen, just above the pubic bone, to help dislodge the baby’s anterior shoulder.
If these first-line techniques are not successful, healthcare providers may then use internal rotation maneuvers, such as the Rubin or Woods screw maneuvers, where a hand is inserted into the vagina to rotate the baby’s shoulder. Another option is to deliver the baby’s posterior arm, which can create more space for the shoulders to pass.
Potential Short and Long-Term Effects
Shoulder dystocia, despite prompt management, can lead to potential complications for both the baby and the mother. For the baby, one of the most recognized risks is brachial plexus injury. This involves damage to the network of nerves that control movement and sensation in the arm and hand, sometimes resulting in a condition called Erb’s palsy. While concerning, most brachial plexus injuries are transient and resolve within months, with less than 10% resulting in permanent injury.
Another possible injury for the baby is a clavicle (collarbone) fracture, which can occur as the shoulder is freed. These fractures typically heal well without long-term issues. In rare, severe cases of prolonged impaction, oxygen deprivation to the baby can occur, leading to more serious outcomes like hypoxic-ischemic encephalopathy.
For the mother, potential complications include postpartum hemorrhage, which is excessive bleeding after delivery, and vaginal or perineal tears that can extend into the anal sphincter. These maternal injuries typically require repair and can impact recovery.