NEW ORLEANS – The link between labor induction and cesarean deliveries was found to be negatively correlated, according to data presented at this year’s Pregnancy Meeting, sponsored by the Society for Maternal-Fetal Medicine.
The findings that a woman’s odds of delivering by C-section are 30% greater (confidence interval, 1.26-1.31; P = less than .01) if she delivers at a hospital with low rates of labor induction, independent of other obstetric risk factors and hospital characteristics, were unexpected by the study’s presenter, Dr. Sarah E. Little of Brigham and Women’s Hospital in Boston. "I was quite surprised by the findings. It suggests to me that inductions themselves may not be the culprit behind the rising rate of cesarean delivery in the United States."
Dr. Little and her colleagues conducted the research to help close the gap between this commonly held belief that an overreliance on induction is at least in part responsible for why the rate of C-section deliveries performed in the United States rose from 20.7% in 1996 to 32.8% in 2011, making it the most commonly performed surgical procedure in the nation. The increased risk has not been shown in prospective trials because the control group would be women with expectant management, according to Dr. Little.
"In retrospective trials, the comparison group is often spontaneous labor, but you can’t choose to be in spontaneous labor," she said. "During expectant management, things can arise – the babies get bigger, the placentas get worse, moms can develop bleeding or preeclampsia – all of which increase the risk of cesarean section, so if you don’t take this into account, then inductions look worse."
For the study, Dr. Little and her colleagues calculated hospital rates of C-sections using the 2010 Nationwide Inpatient Sample of 813,693 deliveries at 604 hospitals. The sample was representative of roughly 20% of all American hospitals, according to Dr. Little and included women at low risk for emergency C-section, and those with no preexisting comorbidities.
The investigators classified hospital level inductions as any induction; low-risk inductions, excluding anyone with preexisting comorbidities; and elective inductions if they were performed when not medically indicated, according to Joint Commission guidelines.
Hospitals in the study were characterized according to location, number of beds, and whether they were teaching facilities. Hospitals that performed fewer than 100 C-sections or did not perform labor inductions were excluded.
The researchers then conducted unadjusted and adjusted hospital cesarean rates according to hospital induction quartile. They also conducted a logistic regression analysis across quartiles to determine the correlation between the hospital rate of induction and the individual’s risk for C-section.
Dr. Little and her team found that hospitals had an average cesarean rate of 31%, with a range of 5.1%-75.7% (mean, 30.5%); rates of labor induction varied from 0% to 50% (mean 19.1%).
Hospitals with high induction rates had lower cesarean delivery rates (Pearson, –0.18; P = less than .001), a negative correlation that held even when only low-risk C-sections and low-risk inductions were studied (Pearson –0.31; P = less than .001). Hospitals in the highest quartile of labor inductions had an average cesarean rate of 32.6%, compared with 29.7% at hospitals in the lowest quartile of inductions.
"There is wide variation in the induction rates across hospitals," said Dr. Little. "I think this speaks to the wide variation in physician practices across the U.S."
The findings were presented during a time when the society is actively encouraging physicians to think twice before inducing labor and is conducting workshops that specifically draw a connection between the two procedures. "This study provides helpful information, and is potentially reassuring to those who require labor induction, but I would continue to encourage a practice of limiting labor induction to those with an indication for delivery and no contraindication to labor," Dr. Brian Mercer, the society’s immediate past president, responded when asked about the results.
The society’s suggested protocols are outlined in the paper, "Preventing the first cesarean delivery" (Obstet. Gynecol. 2012;120:1181-93), which includes an algorithm for when to induce labor – typically, only when medically indicated, such as in the case of membrane rupture.
"I think [our study] supports the SMFM initiative as there is clearly a large variation in practice which could potentially be targeted for change," said Dr. Little. "Also, there are other downsides to labor induction – iatrogenic prematurity if done prior to 39 weeks and increased cost and resource utilization. So even if inductions don’t lead to increased cesareans directly, there are a number of reasons you might want to avoid them."