High Cesarean Rates Persist in Obesity Despite Standardized Protocols
NATIONAL HARBOR, MARYLAND — Implementation of a standardized induction of labor protocol had no significant effect on the rates of cesarean delivery in patients with obesity, based on data from more than 5000 individuals.
Previous research has shown that the risk for cesarean delivery increases by 5% with each 1-kg/m2 increase in body mass index (BMI) among nulliparous patients, said Melissa Riegel, MD, of the University of Pennsylvania, Philadelphia, in a presentation at the meeting sponsored by the Society for Maternal-Fetal Medicine. (abstract 82).
Research on the relationship between obesity and higher cesarean delivery rates “has been clouded by the inability to reduce variation in care,” Dr. Riegel said at the meeting sponsored by the Society for Maternal Fetal Medicine. Failed induction of labor (IOL) is a leading indicator for cesarean delivery, and cesarean delivery is 80% more likely in patients with obesity undergoing IOL than in normal-weight patients, Dr. Riegel said.
Possible explanations for these differences include provider factors such as variability in care management, conscious and unconscious biases, or physiologic differences in patients with obesity such as elevated hormones, differences in the labor curve, and higher doses of oxytocin and prostaglandins, Dr. Riegel said.
Dr. Riegel and colleagues hypothesized that differences in cesarean delivery rates would persist despite a standardized labor induction protocol, thereby supporting the effects of factors other than variations in care on increased cesarean delivery risk after IOL in patients with obesity.
The researchers reviewed data from two sites comparing 2-year periods before and after implementation of an IOL protocol from 2018 to 2022. The study population included nulliparous women with singleton pregnancies at term who underwent IOL with intact membranes and unfavorable cervices, and had a BMI of at least 30 kg/m2 at delivery. The preimplementation group (PRE) included 2480 individuals and the postimplementation group (POST) included 2651 individuals. Patients were divided into weight classes based on BMI: 30-34.9; 35-39.9; ≥40.
The standardized protocol consisted of active labor management with cervical exams, with an amniotomy by the time of the first exam with 4 cm or greater cervical dilation, and further intervention with medication such as oxytocin or an intrauterine pressure catheter if no cervical change was noted after 2 hours.
In a multivariate analysis, the overall cesarean delivery rate was 24.9% before the protocol implementation and 26.0% in the postimplementation group. There were no differences in the risk of cesarean delivery in any obesity class from the PRE to POST period. In addition, no significant differences appeared in the secondary outcomes of duration of labor, maternal morbidity, or neonatal morbidity, Dr. Riegel said. Nonreassuring fetal heart rate tracing was the most common reason for cesarean delivery across all obesity classes and the PRE and POST groups. Study limitations included the use of data from only two sites, but the results were strengthened by the large sample size, said Dr. Reigel. The results indicate that reducing variation in IOL management had no significant effect on the relationship between obesity and cesarean delivery and support underlying physiologic explanations, she said.
Making the Case for Physiology
“By standardizing induction practices, we were able to minimize differences in care and better answer why the increased cesarean delivery rate exists in this patient population,” Dr. Riegel said in an interview. The findings were in line with the primary hypothesis that standardized induction would not affect cesarean delivery rates in patients with obesity, she said. Instead, the findings support potential physiologic differences as “the driving force behind this relationship,” she added. Looking ahead, “There is a role for translational work to investigate the specific biological changes in patients with obesity that might contribute to an increased risk of cesarean delivery and there is also a role for investigating the effectiveness of different labor induction interventions specifically in patients with obesity,” Dr. Riegel said.
Different Induction Protocols Needed for Obese Patients?
“Given that severe maternal morbidity and mortality are continuing to increase in the United States, this study is critical, as we know that both cesarean delivery and obesity are driving factors in increasing maternal morbidity,” said Marissa Platner, MD, a maternal-fetal medicine specialist at Emory University, Atlanta, Georgia, in an interview.
However, the novel takeaway message from the current study is that patients with obesity were more likely to require cesarean delivery even with a protocol in which variation in labor induction techniques are minimized, said Dr. Platner, who was not involved in the study. “This leads to the question of [whether] we should have different standards or protocols for our patients with obesity, as well as a need for clear counseling for these patients early on in pregnancy,” she said. As for further research, “It would be interesting to see if the risk of cesarean delivery changed based on class of obesity, and the primary drivers of cesarean delivery in this study,” Dr. Platner said. “Additionally, it would be helpful to know how much pitocin was needed for patients, based on their BMI category, to achieve successful vaginal delivery,” she noted. The study was supported by a grant from the Eunice Kennedy Shriver National Institute of Child Health and Development. The researchers had no financial conflicts to disclose. Dr. Platner had no financial conflicts to disclose.