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Summary Table

Feature	Detail
Risk Factors	Fetal macrosomia (estimated fetal weight >4,000 g, or >4,500 g in diabetic mothers), maternal gestational diabetes or obesity, prior shoulder dystocia, prolonged second stage of labor, operative vaginal delivery (vacuum/forceps), post-term pregnancy, excessive maternal weight gain
Etiology	Impaction of the anterior fetal shoulder behind the maternal pubic symphysis after delivery of the fetal head, preventing completion of delivery with normal downward traction
Patient Presentation	The fetal head delivers but immediately retracts against the perineum ("turtle sign"); the body does not follow with the next contraction despite gentle downward traction
Classic Physical Exam	Turtle sign (retraction of the fetal head into the perineum after delivery), failure of external rotation and descent of the anterior shoulder, visible distress as the head remains tightly applied against the vulva
Key Diagnostic Results	This is a clinical diagnosis made at the time of delivery. No lab or imaging test confirms it in real time. Postnatally, examine the neonate for Erb palsy (C5-C6), clavicular or humeral fracture, and brachial plexus injury
Management	McRoberts maneuver (hyperflexion of maternal thighs) combined with suprapubic pressure is the first-line intervention. If this fails, proceed to rotational maneuvers (Wood corkscrew, Rubin II) or delivery of the posterior arm. Zavanelli maneuver (cephalic replacement followed by cesarean section) is a last resort
Keywords	Turtle sign, McRoberts maneuver, suprapubic pressure, Erb-Duchenne palsy, brachial plexus injury, macrosomia, diabetic mother

1. Pathophysiology

Shoulder dystocia occurs when the bisacromial diameter (the distance between the two fetal shoulders) is too large to pass through the anteroposterior diameter of the pelvic inlet. In the normal mechanism of labor, after the head delivers, the shoulders rotate into the anteroposterior plane and slide beneath the pubic symphysis. In shoulder dystocia, the anterior shoulder becomes impacted behind the pubic symphysis, halting further descent.

The head delivers normally because it can mold and flex to fit the pelvis, but the shoulders are rigid bony structures that cannot compress. Once the head is out and the anterior shoulder is trapped, the fetal chest is compressed within the birth canal. This compression of the umbilical cord between the fetal body and the pelvic wall creates a time-sensitive emergency because fetal oxygenation rapidly deteriorates. From this point, the obstetric team has a narrow window (generally cited as approximately 4 to 8 minutes) before the risk of irreversible hypoxic injury or death increases substantially.

The reason this condition preferentially injures the brachial plexus is mechanical: when excessive lateral traction is applied to the fetal head to free the trapped shoulder, the ipsilateral C5-C6 nerve roots are stretched. This results in Erb-Duchenne palsy, presenting as the classic "waiter's tip" posture (the arm is adducted, internally rotated, with the forearm pronated and wrist flexed). In more severe traction injuries, the lower brachial plexus (C8-T1) can also be damaged, producing Klumpke palsy (loss of hand grip, "claw hand"). Fractures of the clavicle or proximal humerus can also occur and are sometimes created intentionally as a last-resort maneuver to reduce the bisacromial diameter.

The pathophysiology also explains why gestational diabetes is the single most important maternal risk factor: chronic fetal hyperinsulinemia in response to maternal hyperglycemia causes disproportionate fat deposition around the fetal trunk and shoulders relative to the head, creating the size mismatch that leads to impaction.

2. Classification and Clinical Manifestation

Shoulder dystocia does not have a formal staging or grading system like many other conditions. However, it is clinically useful to categorize it by severity and by the maneuvers required to achieve delivery:

Category	Description	Clinical Implication
Mild (resolved with first-line maneuvers)	Anterior shoulder disimpacts with McRoberts maneuver and suprapubic pressure alone	Typically short duration, lower risk of neonatal injury
Moderate (requires second-line maneuvers)	First-line maneuvers fail; rotational maneuvers (Wood corkscrew, Rubin II) or delivery of posterior arm is required	Longer head-to-body delivery interval, higher risk of brachial plexus injury and fractures
Severe (requires heroic intervention)	All standard maneuvers fail; Zavanelli maneuver (cephalic replacement and cesarean) or intentional clavicular fracture is performed	High risk of fetal hypoxia, permanent nerve injury, or perinatal death; also high maternal morbidity

Neonatal Complications

Complication	Mechanism	Presentation
Erb-Duchenne palsy (C5-C6)	Lateral traction on the neck stretching upper brachial plexus roots	Arm adducted, internally rotated, forearm pronated, wrist flexed ("waiter's tip")
Klumpke palsy (C8-T1)	Severe or upward traction injuring lower brachial plexus	Loss of hand grip, "claw hand," possible ipsilateral Horner syndrome (ptosis, miosis, anhidrosis)
Clavicular fracture	Direct compression against the pubic symphysis or intentional fracture during delivery	Crepitus, asymmetric Moro reflex, pseudoparalysis of the affected arm
Humeral fracture	Traction or manipulation during delivery of the posterior arm	Swelling, tenderness, inability to move the arm
Hypoxic-ischemic encephalopathy	Prolonged cord compression during the impaction interval	Altered tone, seizures, encephalopathy in the neonate

Maternal Complications

Complication	Mechanism
Postpartum hemorrhage	Uterine atony from prolonged second stage, cervical/vaginal lacerations
Third- or fourth-degree perineal tears	Aggressive maneuvers, large episiotomy
Uterine rupture	Rare, associated with Zavanelli maneuver or excessive fundal pressure

3. Diagnostic Workup

Test	Role	Key Finding
Clinical recognition at delivery	Only diagnostic method	Turtle sign, failure of shoulder descent after head delivery
Prenatal ultrasound (estimated fetal weight)	Risk stratification (not diagnostic)	Estimated fetal weight >4,000 g (or >4,500 g in diabetics) raises suspicion but has poor positive predictive value
Postnatal neonatal exam	Identify complications	Assess for Erb palsy, clavicular fracture, humeral fracture, signs of hypoxia
Neonatal imaging (X-ray, if indicated)	Confirm bony injury	Clavicular or humeral fracture
Neonatal MRI or nerve conduction studies	Evaluate persistent brachial plexus injury	Used if palsy does not resolve within weeks

Shoulder dystocia is an intrapartum clinical diagnosis. There is no prenatal test that definitively predicts it. This is a commonly tested concept: ultrasonographic estimation of fetal weight is unreliable for predicting shoulder dystocia, with a false positive rate exceeding 50% for macrosomia. The exam will test whether you understand that ultrasound alone is not an indication for cesarean delivery purely based on estimated fetal weight in the general population. Current guidelines recommend consideration of elective cesarean only when the estimated fetal weight exceeds 5,000 g in non-diabetic women, or exceeds 4,500 g in diabetic women.

The best initial "test" is simply recognizing the clinical scenario: the fetal head delivers, retracts (turtle sign), and the shoulders do not follow. There is no confirmatory test because the diagnosis is self-evident at the bedside. The exam will never ask "what is the best imaging study to confirm shoulder dystocia?" Instead, it will test your ability to recognize the clinical scenario and immediately proceed to management.

Postnatally, the diagnostic focus shifts to the neonate. The examiner should assess the Moro reflex (asymmetric Moro suggests clavicular fracture or brachial plexus injury), passive range of motion, grip strength, and overall neurologic status.

4. Management and Treatment

Step	Intervention	Details
1. Call for help	Activate the obstetric emergency team	Notify senior obstetrician, anesthesiologist, neonatologist, and additional nursing staff
2. McRoberts maneuver	Sharply flex the maternal thighs onto the abdomen	Straightens the lumbosacral angle, rotates the pubic symphysis cephalad, increases the functional AP diameter of the pelvis. This alone resolves approximately 40-50% of cases
3. Suprapubic pressure	Apply firm, continuous or rocking pressure just above the pubic symphysis directed posteriorly	Pushes the anterior shoulder underneath the symphysis. Applied simultaneously with McRoberts. Never apply fundal pressure (this worsens impaction)
4. Rotational maneuvers	Rubin II: pressure on the posterior aspect of the anterior shoulder to adduct and rotate it anteriorly. Wood corkscrew: pressure on the anterior aspect of the posterior shoulder to rotate it 180 degrees	Changes the orientation of the bisacromial diameter to an oblique plane, freeing the impaction
5. Delivery of the posterior arm	Reach into the vagina, flex the posterior elbow, sweep the forearm across the fetal chest, and deliver the posterior hand and arm	Reduces the bisacromial diameter by approximately 20% (equivalent to an arm width). Higher success rate than rotational maneuvers but also higher risk of humeral fracture
6. Gaskin maneuver (all-fours position)	Roll the mother onto her hands and knees	Gravity-assisted change in pelvic geometry. Not commonly tested but recognized as a valid option
7. Zavanelli maneuver	Push the fetal head back into the vagina (cephalic replacement) and proceed to emergency cesarean section	Absolute last resort. Requires general anesthesia, terbutaline or nitroglycerin for uterine relaxation. Significant maternal morbidity
8. Intentional clavicular fracture	Deliberately fracture the anterior clavicle to reduce shoulder width	Technically difficult, rarely performed, but accepted as a final option before Zavanelli

The first and most important step upon recognizing shoulder dystocia is to call for help and avoid panic-driven excessive traction on the fetal head, which is the mechanism that causes brachial plexus injury. Gentle, controlled downward traction is acceptable, but forceful pulling is contraindicated.

McRoberts maneuver combined with suprapubic pressure is always the first intervention and resolves the majority of cases. This pair should be performed simultaneously. If this fails, the clinician proceeds to internal maneuvers: Rubin II, Wood corkscrew, or delivery of the posterior arm. There is no strict required order among the internal maneuvers; the choice depends on the position of the fetus and the clinician's experience.

A critical exam trap: fundal pressure is absolutely contraindicated in shoulder dystocia. Fundal pressure drives the anterior shoulder further into the pubic symphysis, worsening the impaction and increasing the risk of uterine rupture. The exam will often present a scenario where a nurse or assistant suggests fundal pressure, and the correct answer is always to refuse and apply suprapubic pressure instead. Suprapubic pressure is applied above the pubic bone, directed posteriorly toward the fetal face. Fundal pressure is applied at the top of the uterus and pushes the baby downward, which is the wrong vector entirely.

An episiotomy may be performed to provide more room for the clinician's hand during internal maneuvers, but it does not resolve shoulder dystocia by itself because the obstruction is bony, not soft tissue. The exam may test this distinction.

5. Differential Diagnosis and Distractors

Differential Diagnosis	Why It Is Similar	Key Discriminator
Cephalopelvic disproportion (CPD)	Also involves a mismatch between fetal size and maternal pelvis; both associated with macrosomia and prolonged labor	CPD presents with failure to progress during the first stage of labor (cervical dilation arrest). The head does not deliver. In shoulder dystocia, the head delivers successfully but the shoulders are trapped. Timing in the labor course is the key difference
Face or brow presentation	Abnormal fetal presentation causing difficult delivery	Diagnosed during labor by vaginal exam revealing abnormal landmarks (mentum, frontal bone). The head itself has difficulty delivering, whereas in shoulder dystocia the head delivers normally
Uterine rupture	Sudden obstetric emergency during labor with fetal distress	Presents with loss of uterine contraction pattern, severe abdominal pain, fetal bradycardia, and possible vaginal bleeding. There is no "turtle sign" and the head has typically not yet delivered
Nuchal cord (tight)	Can cause the head to retract against the perineum, mimicking the turtle sign	A tight nuchal cord is identified by palpation around the fetal neck after the head delivers. Once the cord is reduced (slipped over the head or clamped and cut), delivery proceeds normally without the need for shoulder dystocia maneuvers
Locked twins	Difficulty delivering the body after the head in a twin pregnancy	Occurs in twin gestations (first twin breech, second twin vertex) where the chins lock. History of twin gestation and breech presentation of the first twin distinguish this scenario

6. Traps and High-Yield Pearls

The single most commonly tested trap on this topic is the distinction between suprapubic and fundal pressure. The exam will frequently describe a scenario where the fetal head has delivered and retracted, then ask for the next best step. The wrong answer is fundal pressure; the correct answer is McRoberts maneuver with suprapubic pressure. Many students confuse these because both involve pressing on the maternal abdomen, but they are applied at completely different locations and produce opposite effects.

A second common trap involves risk factor recognition. The exam may present a diabetic mother with an estimated fetal weight of 4,600 g and ask whether elective cesarean should have been offered. The answer is yes for diabetic women with estimated fetal weight exceeding 4,500 g, and the threshold is higher (5,000 g) for non-diabetic women. Students who do not know these thresholds will get this question wrong.

Another tested concept is complication recognition. The exam may show a newborn after a difficult delivery with the arm hanging limply at the side, internally rotated, with an absent biceps reflex but intact hand grip. This is Erb palsy (C5-C6), not Klumpke palsy. The distinguishing feature is that hand function is preserved in Erb palsy and lost in Klumpke palsy.

Finally, understand that shoulder dystocia is unpredictable and unpreventable in many cases. Up to half of all cases occur in fetuses with normal estimated weight and without identifiable risk factors. The core competency being tested is not prediction but recognition and correct sequencing of maneuvers: McRoberts and suprapubic pressure first, internal maneuvers second, heroic interventions last. The exam rewards candidates who know the algorithm and can apply it under time pressure without resorting to harmful interventions like fundal pressure or excessive traction.

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