Dual mechanism responsible for brachial plexus injuries

OBJECTIVE: To define the maternal, neonatal and labor characteristics associated with obstetrical biachial plexus injuries in the presence and absence ol shoulder dvstocia and to determine the incidence of residual paraKsis. STUDY DESIGN: Medical i erords of neonates with a discharge diagnosis of brachial plexus injury were reviewed for the interxal ot 1991-1995. Data were tabulated loi' maternal, neonatal and labor characteristics including the presence or absence ol documented shoulder dvstocia. Using T-test and square lest, patients with documented shoulder dvstocia were compared to those without shoulder dvstocia. RESULTS: 36 neonates sustained brachial plexus injuries among '20,1175 livebirths (1.7 / 1000 births). 6 cases were excluded from comparison because of abnormal presentation or other confounding variables. In 17 rases a shoulder dystocia was documented while in 13 cases no shoulder dvstocia was identified. Neonates with shoulder cKstocia were statistically larger, had lower one minute Apgar scores, were more likely to be spontaneously delivered arid die right brachial plexus was more ol'ten injuied. Those without shoulder dvstocia, were more often delivered with forceps and the left brachial plexus was more often affected. In 6 cases parahsis was e\ident at the last visit however onlv one was followed more than a vcar. CONCLUSIONS: Among vertex presentations, brachial plexus injuries occur in two cluiicalh disiimt groups of patients. Tin' maternai, neonatal and laboi characteristics oi maternal neonatal pairs with obstetrical brachial plexus injuries are different for pairs that experience shoulder dvstocia uhen compared with those That do not. Different mechanisms of injnn appear lo be operative in tlie shoulder dvstocia group \ersus the nonshoulder dvstocia group. Adverse fetal outcome and residual paraivsis is uncommon in all groups.