Risk of recurrent shoulder dystocia: are we any closer to prediction?

Objective: To determine the incidence and risk factors for recurrent shoulder dystocia in women. Methods: We searched Medline, Pubmed, Embase, and CINAHL for relevant articles in English and French from 1980 to February 2018 that described risks of recurrent shoulder dystocia undergoing a trial of labour in subsequent pregnancies. A total of 684 articles were found, of which 13 were included as they met criteria. We extracted data on study characteristics, incidence of recurrent shoulder dystocia, degree of neonatal injury, and presence of known risk factors. Results: There was a wide variation in the incidence of shoulder dystocia in subsequent pregnancies from 1-25%. The largest cohort reported a risk of 13.5%. The most important risk factor for recurrent shoulder dystocia is an increase in birthweight in the subsequent pregnancy compared to the index pregnancy (OR 7-12). Prolonged second stage, instrumental delivery, maternal diabetes, increased maternal BMI, and severe neonatal morbidity in the index pregnancy were also associated with an increased risk of recurrent shoulder dystocia. However, many of these risk factors were present in women who did not have a recurrent shoulder dystocia. In addition, women with recurrent shoulder dystocia rarely had identifiable risk factors, other than the history of previous shoulder dystocia. Sample sizes were low as most studies are single centre, retrospective cohorts with low rates of subsequent pregnancy and vaginal birth as many women may have elected to have a caesarean section in subsequent pregnancies or were lost to follow up. There was a high rate of reporting bias and heterogeneity, prohibiting formal meta-analyses. Conclusion: Recurrent shoulder dystocia is an unpredictable obstetric complication with potentially devastating consequences. Individual assessment and thorough counselling should be offered to women contemplating a subsequent planned vaginal birth with specific attention paid to those women where the estimated birthweight is >4000 g or greater than in the index pregnancy.