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Anything out of the ordinary that occurs during childbirth can be frightening. One uncommon occurrence is shoulder dystocia, which occurs when a baby’s head emerges from the birth canal but the baby’s trunk ceases to progress because the baby’s shoulder is lodged behind the pubic symphysis, or the joint between the left and right pubic bones through which the baby must pass to enter the birth canal.
Shoulder dystocia is a time-sensitive medical emergency, because if the situation is not resolved within 4-6 minutes, the baby can sustain neurologic injury, partial paralysis, or even death from lack of oxygen (hypoxia). The incidence of shoulder dystocia is relatively rare — between 0.2% and 3% of births.
Complications from shoulder dystocia also are infrequent and are successfully resolved most of the time. Infants may suffer fractured humerus or clavicle, brachial plexus injury, asphyxia, and/or umbilical cord compression. Less than 10% of babies affected by shoulder dystocia sustain permanent injury. For mothers, possible complications include severe hemorrhage and tissue lacerations to the cervix, rectum, uterus, or vagina.
Brachial plexus injuries (BPI), which occur in 4-16% of shoulder dystocia deliveries, are the most serious. A BPI occurs when the network of nerves that transmits signals from the spine to the shoulder, arm, and hand are stretched, compressed, torn, or completely severed from the spinal cord. Fortunately most cases of shoulder dystocia-related BPI resolve without any permanent disability.
Risk factors for shoulder dystocia delivery include:
• a very large baby (macrosomia);
• maternal obesity;
• maternal diabetes;
• multiple births such as twins or triplets (multiparity);
• late gestation; and
• past delivery with shoulder dystocia.
Shoulder dystocia, for the most part, is unpredictable and rarely preventable. It can happen with any delivery. In fact, up to half of shoulder dystocia cases had no association with known risk factors. And though macrosomia may be diagnosed beforehand, an estimated 84% of women who experience shoulder dystocia don’t have prenatal diagnoses of macrosomia. About 12% of women with a history of shoulder dystocia experience a recurrence in subsequent pregnancies.
Cases of shoulder dystocia necessitate an immediate, coordinated, multidisciplinary response that applies evidence-based algorithms to achieve the most favorable outcomes. Once shoulder dystocia is detected, the obstetrician should summon assistance from other clinicians. The time is noted and kept with announcements to the team at various progression intervals.
The woman in labor is told not to push while several recognized approaches are attempted to safely dislodge the baby. One of the most common is the McRoberts maneuver, in which the mother’s legs are pushed up against her abdomen to flatten and rotate the pelvis, allowing the baby to pass through more easily. If that doesn’t work, an experienced clinician will manually apply suprapubic pressure just above the fetal anterior shoulder, midline between the left and right pubic bones. Sometimes these two interventions are executed in combination. The McRoberts maneuver is successful 42% of the time. Combined with suprapubic pressure, it resolves 54% of shoulder dystocias.
After these steps have been taken without success, the obstetrician will attempt an internal rotation of the baby or try to extract the posterior arm from the birth canal. Sometimes women are instructed to get on their hands and knees to ease the baby’s exit through the pubic bones. A last resort would be the Zavenelli maneuver, in which the baby’s head is pushed back into the birth canal so an emergency cesarean can be performed.
It is important to keep in mind that shoulder dystocia is rare, and complications from it even rarer. Expectant women who aren’t sure about their risk should address questions about shoulder dystocia to their obstetrician.
This blog provides general information and discussion about healthcare-related subjects. The content and linked materials provided are not intended and should not be construed as medical advice. If the reader is an expectant mother with a medical concern, she should consult with an appropriately licensed physician or healthcare provider.
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