Risk of Instrumental Delivery in Maternal Obesity: Estimates With Measures of Effect Size

Background: Obesity, defined as a body mass index ≥30 kg/m², is epidemic in the United States and is associated with increased risks of adverse events. Studies have examined the role of maternal obesity on the incidence of instrumental vaginal delivery, but the results are divided. However, these analyses used frequentist tests that risk false discovery. The purpose of this retrospective study was to quantify the association of maternal obesity to the need for instrumental delivery with measures of effect size. Measures of effect size allow assessment of the impact of clinical risk factors on outcomes of interest. Methods: All parturients aged ≥18 years in active labor at our facility from January 2018 to May 2019 were entered into this study. Patient demographics, previously reported comorbidities, and obstetric parameters were collected and analyzed to determine the clinical impact of maternal obesity on the incidence of instrumental delivery. One effect size measure, risk differences, was used to quantify the clinical effect of maternal obesity on the need for instrumental delivery. A generalized linear model was used to standardize the measures of effect size of previously reported comorbidities, including maternal obesity, and to determine their association with the need for instrumental delivery. Results: The incidences of chronic and gestational hypertension, preeclampsia, chronic diabetes, and reactive airway disease were higher in parturients with maternal obesity. Risk differences due to maternal obesity were observed in parturients presenting with shoulder dystocia but not in those who underwent oxytocin induction or in nulliparous parturients. Following regression analysis, maternal obesity did not clinically impact the need for instrumental delivery. Conclusion: These findings suggest that maternal obesity did not have a clinical impact on the need for instrumental delivery.