Rising trends in the incidence of shoulder dystocia and development of a novel shoulder dystocia risk score tool: a nationwide population-based study of 800 484 Finnish deliveries

Introduction Shoulder dystocia has remained an unpredictable and feared emergency in obstetrics. Some risk factors have been identified but nevertheless there is a lack of risk evaluation tools in clinical practice. The aim of this study was to evaluate the incidence and risk factors of shoulder dystocia in the Finnish population and to develop a shoulder dystocia risk score tool. Material and methods This retrospective, population-based study included all deliveries in Finland between 2004 and 2017 (n = 800 484). The annual numbers of shoulder dystocia diagnoses were gathered from nationwide Finnish Medical Birth Register and Hospital Discharge Register. The incidence of shoulder dystocia was calculated in subgroups according to the mode of delivery, maternal diabetes status, body mass index (BMI), age, parity and gestational age. Based on these numbers, a shoulder dystocia risk score tool was created. Results The overall incidence of shoulder dystocia was 0.18%. It increased significantly during the study period from 0.10% to 0.32% (P < .001). More specifically, the incidence increased significantly in all analyzed subgroups except for women with BMI <18.5 or age <20 years. To evaluate the importance of risk factors, practical and simple shoulder dystocia risk score tool was created. Instrumental vaginal delivery, maternal diabetes of any kind, BMI >= 25, age >= 40 years and gestational age >= 41 weeks were associated with higher shoulder dystocia risk compared with non-diabetic, non-obese and younger women with spontaneous deliveries before 41 weeks of gestation. In our risk score tool, cases with shoulder dystocia had a significantly higher number of risk points than those without it (15.2 vs 10.4, P < .001). The risk was significantly high when the scores were >= 18 points (relative risk 9.54, 95% confidence interval 8.61-10.57). Conclusions The incidence of shoulder dystocia in Finland increased during the study period but it is still low compared with previous studies from other countries. In clinical daily practice, the new shoulder dystocia risk score tool helps to evaluate the individual risk profile of the parturient. According to this risk score tool, the highest risk was found with the combination of instrumental vaginal delivery, maternal diabetes, BMI >= 25, age >= 40 years and gestational age >= 41 weeks.