Infant Brachial Plexus Injuries: When to Refer Immediately and When to Wait

Apurva S. Shah, MD, MBA


April 30, 2019

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Risk Factors

Typically, this injury occurs in a larger baby, with a weight of 10 lb or more. These infants are often born to a mother who is postdates or has gestational diabetes. Most women are primiparous, rather than nulliparous, with a size mismatch between the width of the baby's shoulders and the size of the outlet of the maternal pelvis, resulting in shoulder dystocia. For the obstetrician, that's an emergency, because the baby might be hypoxic and the speed of delivery is very important in preventing anoxic brain injury as well as for the baby's overall health. But the shoulder dystocia can create stress injury to the brachial plexus.

What has really changed over the past 15 years is the type of baby that's being born. With the increase in women receiving fertility interventions, there are more twin or triplet pregnancies, with babies with a smaller birthweight. Even for mothers who have a singleton pregnancy, labor induction is happening at an earlier time during pregnancy, so the babies are smaller at the aggregate national level. As well, the rate of cesarean section has gone up pretty substantially. Cesarean section is protective for brachial plexus injuries, because there is typically no risk for the shoulder to get stuck during delivery. The rate of cesarean section went up during the study period, from about 20% of all deliveries in 1997 to over one third of deliveries in 2012.

Interestingly, that intuitive feeling that because obesity rates in the adult population are increasing, then maybe we would be delivering babies of a higher birthweight, doesn't seem to be true.

However, even when a baby is delivered vaginally and shoulder dystocia is present, the risk of having a brachial plexus injury has dropped. The risk for brachial plexus injury during shoulder dystocia used to be about 11%, but it's dropped to about 8% over the past 15-20 years.

Something has changed in obstetric training and delivery proficiency. There is no study examining which specific obstetric training techniques have resulted in this decrease. I know that at a lot of centers, there has been increased focus on simulation training for shoulder dystocia.