Shoulder dystocia is the failure of the shoulders to spontaneously traverse the pelvis after delivery of the fetal head. It is an obstetric emergency. It occurs due to impaction of the shoulder behind the pubic symphysis.
It should be suspected when the fetal head retracts into the perineum (ie, turtle sign) after expulsion due to reverse traction from the shoulders being impacted at the pelvic inlet.
Anterior obstruction is more common than posterior obstruction.
If descent of the fetal head continues while the anterior or posterior shoulder remains impacted, then stretching of the nerves in the brachial plexus may occur and may result in nerve injury.
Risk factors: High birth weight (> 4000 g), maternal diabetes mellitus, previous shoulder dystocia, postterm pregnancy, male fetal gender, maternal obesity, advanced maternal age
The goal of the management is to prevent fetal asphyxia, brachial plexus injury.
Ask the patient to stop pushing, drain the bladder, perform episiotomy.
McRoberts Maneuver: Flex the thighs against the abdomen to flatten the sacrum to remove the sacral promontory as an obstruction site.
If McRoberts Maneuver is unsuccessful, try posterior arm delivery.
Still unsuccessful, try rotational maneuver (Woods, Rubin)
Last resort: Gunn-Zavanelli-O’Leary maneuver: Replacement of the fetal head in the pelvis, followed by cesarean delivery.
Infant: Brachial plexus palsy, clavicular fracture, humerus fracture, hypoxia, encephalopathy, death.
Maternal: Hemorrhea, lacerations
Image credit: By Henry Lerner – https://thewinnower.com/papers/539-the-difficult-delivery-shoulder-dystocia, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=73353284