Shoulder dystocia occurs when one shoulder of the fetus lodges against the woman's pubic bone, and the baby is therefore caught in the birth canal.
The fetus is positioned normally (head first) for delivery, but the fetus's shoulder becomes lodged against the woman's pubic bone as the fetus's head comes out. Consequently, the head is pulled back tightly against the vaginal opening. The baby cannot breathe because the chest and umbilical cord are compressed by the birth canal. As a result, oxygen levels in the baby's blood decrease.
Shoulder dystocia is more common when the fetus is large, particularly when labor is difficult, long, or rapid or when a vacuum extractor or forceps is used because the fetus's head has not fully moved down (descended) in the pelvis. It is also more common when women are obese, have diabetes, or have had a previous baby with shoulder dystocia.
When this complication occurs, the doctor quickly tries various techniques to free the shoulder so that the baby can be delivered vaginally. Sometimes when these techniques are tried, the nerves to the baby's arm are damaged or the baby's arm bone or collarbone may be broken. An episiotomy (an incision that widens the opening of the vagina) may be done to help with delivery. If these techniques are unsuccessful, the baby may be pushed back into the vagina and delivered by cesarean. If all of these techniques are unsuccessful, the baby may die.
Last full review/revision June 2013 by Julie S. Moldenhauer, MD