An objective definition of shoulder dystocia: Prolonged head-to-body delivery intervals and/or the use of ancillary obstetric maneuvers

Objective: To generate an objective definition of shoulder dystocia by timing the events of the second and third stages of labor, and to define the true incidence of shoulder dystocia. Methods: In 34 arbitrarily selected 24-hour time periods, a nonparticipating observer prospectively timed intervals of the second stage of labor in all vaginal deliveries and recorded the use of obstetric maneuvers (McRoberts, episiotomy after delivery of the fetal head, intentional extension of initial episiotomy after delivery of the fetal head, suprapubic pressure, posterior arm rotation to an oblique angle, rotation of the infant by 180°, delivery of the posterior arm, and general anesthesia) and whether the obstetric attendant identified a delivery with shoulder dystocia. All data are reported as mean ± standard error of the mean. Results: Two hundred fifty deliveries were timed and recorded prospectively. Mean intervals (in seconds) in nonmaneuver patients were as follows: head to anterior shoulder 14.8 ± 1.0, anterior to posterior shoulder 3.9 ± 0.6, posterior shoulder to body 5.4 ± 0.8, and total head-to-body time 24.2 ± 1.3. Three groups of patients were defined after delivery. The maneuver group consisted of 27 patients requiring any of the aforementioned obstetric maneuvers, although the obstetric attendant identified only 16 of these as shoulder dystocia. The prolonged delivery group included 29 patients with the head-to-body delivery interval exceeding the mean plus two standard deviations (60 seconds) of nonmaneuver patients. Sixteen of the 27 maneuver patients were identified as prolonged. The 210 not identified as maneuver or prolonged were considered to be normal. Normal patients had a significantly lower newborn birth weight (3269 ± 38 g), and a lower proportion of 1-minute Apgar scores of 7 or less (11%) than did the maneuver (4247 ± 86 g, 41%) and prolonged groups (3952 ± 118 g, 34%). Defining shoulder dystocia as a prolonged head-to-body delivery time and/or the use of obstetric maneuvers identified 40 patients who had birth weights and 1-minute Apgar scores significantly different from the normal patients. Conclusion: The incidence of shoulder dystocia, as defined by the use of ancillary obstetric maneuvers, is higher than that reported previously, and the reporting of shoulder dystocia appears to be unreliable. The interval from head-to-body delivery is delayed significantly in patients with shoulder dystocia, despite the lack of recognition of shoulder dystocia. We propose defining shoulder dystocia as a prolonged head-to-body delivery time (eg, more than 60 seconds) or the need for ancillary obstetric maneuvers.