Neonatal Brachial Plexus Palsy and causation

A vaginal childbirth is the result of the internal (endogenous) expulsive forces of uterine contractions, usually supplemented by active maternal pushing1. Depending on the clinical circumstances, additional external (exogenous) traction forces may be required from the birth attendant. This blend of internal and external forces varies from birth to birth. Women who have had a previous vaginal delivery, for example, may deliver successfully with uterine contractions alone and the role of the birth attendant may be simply to control and slow the delivery so that trauma to the maternal perineum from stretching by the fetal head is minimised. In contrast, additional traction may be required by an obstetrician at the time of an operative vaginal delivery for fetal distress or dystocia. The strength of the traction required may be increased by clinical factors, for example, fetal macrosomia or malposition. The traction should be axial in the direction of the birth canal, which is a vector combining horizontal and vertical traction at 25-45 degrees below the horizontal when the woman is in the lithotomy position.