Predictors of shoulder dystocia at the time of operative vaginal delivery: a prospective cohort study

Incidence of shoulder dystocia and risk factors for recurrence in the subsequent pregnancy-A historical register-based cohort study

INTRODUCTION

Shoulder dystocia is a rare obstetric complication, and the risk of recurrence is important for planning future deliveries.

MATERIAL AND METHODS

The objectives of our study were to estimate the incidence and risk factors for recurrence of shoulder dystocia and to identify women at high risk of recurrence in a subsequent vaginal delivery. The study design was a nationwide register-based study including data from the Danish Medical Birth Registry and National Patient Register in the period 2007-2017. Nulliparous women with a singleton fetus in cephalic presentation were included for analysis of risk factors in index and subsequent delivery.

RESULTS

During the study period, 6002 cases of shoulder dystocia were reported with an overall incidence among women with vaginal delivery of 1.2%. Among 222 225 nulliparous women with vaginal births, shoulder dystocia complicated 2209 (1.0%) deliveries. A subsequent birth was registered in 1106 (50.1%) of the women with shoulder dystocia in index delivery of which 837 (77.8%) delivered vaginally. Recurrence of shoulder dystocia was reported in 60 (7.2%) with a six-fold increased risk compared with women without a prior history of shoulder dystocia (risk ratio [RR] 5.70, 95% confidence interval [CI]: 4.41 to 7.38; adjusted RR 3.06, 95% CI: 2.03 to 4.68). Low maternal height was a significant risk factor for recurrence of shoulder dystocia. In the subsequent delivery, significant risk factors for recurrence were birthweight >4000 g, positive fetal weight difference exceeding 250 g from index to subsequent delivery, stimulation with oxytocin and operative vaginal delivery. In the subsequent pregnancy following shoulder dystocia, women who underwent a planned cesarean (n = 176) were characterized by more advanced age and a higher prevalence of diabetes in the subsequent pregnancy. Furthermore, they had more often experienced operative vaginal delivery, severe perineal lacerations, and severe neonatal complications at the index delivery.

CONCLUSIONS

The incidence of shoulder dystocia among nulliparous women with vaginal delivery was 1.0% with a 7.2% risk of recurrence in a population where about 50% had a subsequent birth and of these 78% had subsequent vaginal delivery. Important risk factors for recurrence were low maternal height, increase of birthweight ≥250 g from index to subsequent delivery and operative vaginal delivery.

Shoulder Dystocia: A Comprehensive Literature Review on Diagnosis, Prevention, Complications, Prognosis, and Management

The term dystocia refers to labor characterized by a slow progression with delayed rates or even pauses in the dilation of the cervix or the descent of the fetus. Dystocia describes the deviation from the limits that define a normal birth and is often used as a synonym for the term pathological birth. Shoulder dystocia, also known as the manual exit of the shoulders during vaginal delivery on cephalic presentation, is defined as the "failure of the shoulders to spontaneously traverse the pelvis after delivery of the fetal head". This means that obstetric interventions are necessary to deliver the fetus's body after the head has been delivered, as gentle traction has failed. Abnormal labor (dystocia) is expressed and represented in partograms or by the prolongation of the latent phase or by slowing and pausing in the phases of cervical dilatation and fetal descent. While partograms are helpful in visualizing the progress of labor, regular use of them has not been shown to enhance obstetric outcomes considerably, and no partogram has been shown to be superior to others in comparative trials. Dystocia can, therefore, appear in any phase of the evolution of childbirth, so it is necessary to simultaneously assess all the factors that may contribute to its abnormal evolution, that is, the forces exerted, the weight, the shape, the presentation and position of the fetus, the integrity and morphology of the pelvis, and its relation to the fetus. When this complication occurs, it can result in an increased incidence of maternal morbidity, as well as an increased incidence of neonatal morbidity and mortality. Although several risk factors are associated with shoulder dystocia, it has proven impossible to recognize individual cases of shoulder dystocia in practice before they occur during labor. Various guidelines have been published for the management of shoulder dystocia, with the primary goal of educating the obstetrician and midwife on the importance of a preplanned sequence of maneuvers, thereby reducing maternal and neonatal morbidity and mortality.