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Karen Boe Gatlin
Karen Boe Gatlin
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Shoulder Dystocia and Nerve Injury

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Shoulder dystocia can cause injury to the nerves in the brachial plexus, resulting in impaired function of the arm and shoulder. The injury is the result of improper delivery technique by the obstetrician. The shoulders become “stuck” in the birth canal and traction on the brachial plexus to effect delivery may result in permanent nerve damage. Brachial plexus injury has often been assumed to be the result of excessive lateral head flexion applied during delivery, thereby selectively stretching the nerve roots. However, the risks of this injury can be minimized by proper preventive actions.

1) Detect macrosomia (large fetus). The rate of shoulder dystocia increases as fetal weight increases during pregnancy. The physician must detect macrosomia by taking proper measurements consisting of fetal weight, length, occipitofrontal circumference of the head, chest diameter, and shoulder circumference. Heavier infants have larger head chest and shoulder circumference and chest-head differences. Excessive size infants (infants over 4000/4500 grams) are more prone to shoulder dystocia. Ultrasound can correctly identify the presence or absence of macrosomia in 87% of patients. Cesarean section should be performed when ultrasound shows fetal weight to be greater or equal to 4250 grams.

2) Screen for Diabetes Infants of Diabetic mothers show a greater shoulder-head circumference difference. The risk for shoulder dystocia is increased in infants of diabetic women when actual birth weight is greater or equal to 4000 grams. Shoulder dystocia rates in infants of diabetic women are as high at 10% overall and as high as 25% to 50% in macrosomic infants. Serial ultrasounds in Diabetics is advisable. Avoiding vaginal delivery of macrosomic infants of diabetic mothers would decrease shoulder dystocia in this group.

3) Utilize proper delivery techniques When shoulder dystocia occurs, the obstetrician is faced with dilemma of how to deliver the infant quickly without applying forces large enough to cause injury. Pulling or traction will increase the impaction. Twisting the neck leads to neurological damage. The main cause of brachial plexus palsies is forceful stretch together with extreme movements. Brachial plexus injuries occur when there is a strong lateral traction on the head and neck or a downward traction on the shoulders. Extending the episiotomy may assist in delivery in conjunction with proper maneuvers.