https://www.ajog.org/article/S0002-9378(24)01109-8/abstract

Abstract

Background

Shoulder dystocia is associated with neonatal morbidity. Higher maternal prepregnancy body mass index is an established risk factor for shoulder dystocia, yet the relationship between maternal prepregnancy body mass index and resulting neonatal morbidity after shoulder dystocia is not well studied.

Objectives

We assessed the association between body mass index and neonatal adverse outcomes following shoulder dystocia. The frequency and type of maneuvers used to resolve shoulder dystocia by maternal body mass index was compared.

Study Design

We conducted a retrospective cohort study of pregnant individuals who experienced a shoulder dystocia at delivery from June 2012-July 2021 at a tertiary care center. We included singleton non-anomalous livebirths ≥36 weeks’ gestation at a single academic medical center in the Midwestern US. The primary exposure was prepregnancy body mass index categorized as: <30 kg/m² [referent], 30-34.9 kg/m², and ≥35 kg/m². The primary outcome was a composite neonatal morbidity including birth injury (brachial plexus injury or fracture), seizures, hypoxic ischemic encephalopathy, and 5-minute Apgar < 7. Secondary outcomes were neonatal intensive care unit admission and neonatal acidemia (cord arterial pH < 7.10). Shoulder dystocia duration and the number and types of maneuvers were compared by body mass index group. Multivariable logistic regression was used and adjusted for nulliparity, diabetes, operative vaginal delivery, and gestational age.

Results

Among 872 individuals who experienced a shoulder dystocia at delivery, 602 (69.0%) had a body mass index <30 kg/m², 160 (18.3%) had a body mass index between 30-34.9 kg/m², and 110 (12.6%) had a body mass index ≥35 kg/m². The median duration of shoulder dystocia was 40 seconds (interquartile range 30, 60 seconds) and did not vary by maternal body mass index. Deliveries complicated by body mass index ≥35 kg/m² required a greater number of maneuvers compared to those with lower maternal body mass index (p<0.01). McRoberts (96.0%), suprapubic pressure (90.2%) and delivery of the posterior arm (41.1%) were the most frequent maneuvers in all body mass index groups. Rubin’s maneuver was more frequently used with body mass index ≥35 kg/m² compared with body mass index <30 kg/m² (34.6% versus 22.4%, p = 0.02, adjusted odds ratio 1.63, 95% CI 1.04-2.57). Composite neonatal morbidity did not differ by body mass index. Neonatal injury was more frequent with body mass index ≥35 kg/m² compared with body mass index <30 kg/m² (adjusted odds ratio 1.97, 95% CI 1.06-3.68). Interaction between body mass index and number of maneuvers was not statistically significant (p=0.94).

Conclusions

Among pregnant individuals who experienced a shoulder dystocia, increased prepregnancy body mass index was associated with an increased number of maneuvers performed during a shoulder dystocia, but not longer duration. Risk of neonatal injury following shoulder dystocia, but not the composite neonatal adverse outcome, was increased with body mass index ≥35 kg/m².