On redefining shoulder dystocia and at-risk populations

Abstract

To the Editors: Studying brachial plexus injuries over extended periods of time helps gage their temporal incidence and severity. Chauhan et al1Chauhan S.P. Rose C.H. Gherman R.B. Megann E.F. Holland M.W. Morrison J.C. Brachial plexus injury: a 23-year experience from a tertiary center.Am J Obstet Gynecol. 2005; 192: 1795-1800Abstract Full Text Full Text PDF PubMed Scopus (100) Google Scholar did well to study injuries at 1 tertiary center for >20 years and concluded that the risk of injury in general is 1 in 1000 deliveries and that permanent injury is 1 in 10,000 deliveries. This speaks highly for the care provided at the University of Mississippi, because most reports that the authors cite (including their previous one) have a higher incidence of injury, both temporary and permanent. We (and others) report much higher incidences, >6.0 per 1000 deliveries and >1 in 6 per 1000 deliveries, for temporary and permanent injuries, respectively.2Gurewitsch E.D. Johnson E. Hamzehzadeh S. Allen R.H. Risk factors for brachial plexus injury with and without shoulder dystocia.Am J Obstet Gynecol. 2006; 194: 486-492Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar Part of the reason for this discrepancy is the definition of the at-risk population. Instead of using all vaginal deliveries of >500 g as the denominator for calculating incidence, we use a minimum birth weight (typically 2500 g) because shoulder dystocia and injuries occur almost exclusively in that subgroup. The authors report a rate of temporary injuries without shoulder dystocia of approximately 50% during the period 1980 to 1991, contrasting their previous study corresponding to the same time period, which had a 100% association of injury with antecedent shoulder dystocia for cephalic vaginal deliveries. The principal reason for this difference is the definition of shoulder dystocia. In the earlier study, shoulder dystocia deliveries were identified from records so coded, which left the diagnosis to the providers. In the current study, shoulder dystocia was redefined by the authors as “the need for additional obstetric maneuvers beyond gentle traction.” If maneuvers were not done or not documented, deliveries that originally were coded as shoulder dystocia were reclassified as non–shoulder dystocia in the new study. We found that 1 in 8 deliveries that resulted in injury were coded as shoulder dystocia, yet there were no maneuvers documented.2Gurewitsch E.D. Johnson E. Hamzehzadeh S. Allen R.H. Risk factors for brachial plexus injury with and without shoulder dystocia.Am J Obstet Gynecol. 2006; 194: 486-492Abstract Full Text Full Text PDF PubMed Scopus (58) Google Scholar The authors suggest that permanent injury is not associated with shoulder dystocia and cannot be prevented. However, even as currently defined, the rate of shoulder dystocia among the 10 permanent injuries was 80%, which is below nearly all reports on permanent injury and is significant when compared with an expected association without shoulder dystocia of 50% (P = .05). For studies over time, 1 study reports a 4-fold decrease in injury rate over 20 years,3Adler J. Patterson R.L. Erb's palsy: long term results of treatment in eighty-eight cases.J Bone Joint Surg. 1967; 49: 1052-1074PubMed Google Scholar and another study reports an increase in injury rate over extended periods.4Bager B. Perinatally acquired brachial plexus palsy: a persisting challenge.Acta Paediatr. 1997; 86: 1214-1219Crossref PubMed Scopus (138) Google Scholar Respectively, these separate eras correspond to rotational maneuvers being supplanted by the McRoberts' maneuver as first-line treatment of shoulder dystocia. Thus, the conclusion that permanent injury is not amenable to prevention should be viewed with caution.