What is Shoulder Dystocia and What are the Risk Factors?
What is shoulder dystocia?
Shoulder dystocia occurs when, after delivery of an infant’s head, the anterior shoulder (the one pointing up, towards the ceiling) gets stuck behind mom’s pubic bone. Shoulder dystocia can often, but not always, be resolved by the use of any of a number of techniques employed by the physician during delivery. When these techniques do not work, or if too much traction (forceful pulling) is applied to the baby’s head to effect delivery, the bundle of nerves supplying the arm (brachial plexus) can be injured.
Is my baby at risk for shoulder dystocia?
Most babies, even large babies, are delivered without complications.  But, shoulder dystocia can happen to any baby during delivery. Sometimes, it can be predicted, and sometimes it can be prevented. There are a number of conditions that create an increased risk for shoulder dystocia. As the risk for shoulder dystocia increases, the risk of injury to the baby (Erb’s Palsy or Brachial Plexus injury) also increases.
The easiest way to prevent injury caused by shoulder dystocia is to prevent the dystocia. This is done by recognizing the risk factors, which lead to anticipation of the problem, which can then, in turn, lead to prevention.
Risk factors that can be known before and during pregnancy include:
- Maternal birthweight—was mom a big baby herself? Babies who are “large for gestational age" are more likely to get stuck during delivery. 
- Maternal age—women over 40 are more likely to encounter a dystocia. 
- Maternal height—mothers of short stature (less than 5’2") are nearly twice as likely to encounter a dystocia 
- Maternal obesity—this is a very serious risk factor, significantly increasing the incidence of shoulder dystocia 
- Maternal diabetes—women with diabetes tend to have bigger babies, therefore increasing the risk of shoulder dystocia 
- Multiparity—mom has already had at least one baby
- Overdue baby—babies past their due date continue to grow. Bigger babies are more likely to get stuck during delivery. 
- Excessive maternal weight gain during pregnancy—moms who gain 35 pounds or more during pregnancy are at a significantly higher risk for shoulder dystocia, some studies say up to 10x the ordinary risk. 
- Fundal Height— mothers with higher fundal height measurements at term have a higher rate of shoulder dystocia. 
- Fetal Macrosomia— a big baby—bigger than expected for gestational age.
- Abnormal pelvis size or shape—the pelvis is what the baby is most likely to get stuck on. An abnormally sized or shaped pelvis increases this risk.
Risk factors that can be known during delivery include: 
- Abnormal first stage of labor— the time between when the contractions start and when the cervix is fully dilated
- Prolonged second stage of labor— the time between full dilation of the cervix and the baby being born.
- Abnormal descent of baby— the baby is not moving down into the birth canal normally; it is either moving too slow, or not at all, or may start and then stop moving prematurely.
- Need for midpelvic delivery— the use of assistive instruments to deliver the baby, such as forceps and vacuum extraction.
If you believe you have an increased risk for shoulder dystocia, talk to your doctor about your concerns. As about the relative risks to you and your baby in vaginal versus cesarean delivery, and be certain you are listening carefully to the answers you are given.
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 Klebanoff M, Mills, J, Berendes H. Mothers birth weight as a predisctor of macrosomia. Am J Obstet Gynecol 1985; 153:253-8.
 Lehman D, Chism J. Pregnancy outcome in medically complicated and uncomplicated patients aged 40 years and older. Am J Obstet Gynecol 1987; 157:738-44.
 O’Leary J. 2009 Shoulder Dystocia and Birth Injury: Prevention and Treatment 3rd Ed. Humana Press, New Jersey, at pp. 7-8.
 Robinson H, Tkatch S, Mayes A, et al. Is maternal obesity a predictor of shoulder dystocia? Am J Obstet Gynecol 2003; 101:24-7; Weiss J, Malone F, Emig D. et al. Obesity, obstetric complications and cesarean delivery rate—a population-based screening study. Am J Obstet Gynecol 2004; 190:1091-7.
 Weiss J, Malone F, Emig D. et al. Obesity, obstetric complications and cesarean delivery rate—a population-based screening study. Am J Obstet Gynecol 2004; 190:1091-7.
 O’Leary J. 2009, at p. 23.
 Apuzzio J, Ventizileos A, Iffy L. Operative Obstetrics 3rd Ed. London & New York: Taylor & Francis. See also: Boyd ME, Usher RH, McLean FH. Fetal macrosomia: Prediction, risks, proposed management. Obstet Gynecol 1983; 61:715-720; Dor N, Mosberg H, Stern W, et al. Complications in fetal macrosomia. NY State J Med 1984;84:302-9.
 O’Leary J. 2009 at p. 29.
 O’Leary J. 2009 at pp. 49-55.