MINNEAPOLIS - Cesarean delivery rates vary significantly from one hospital to another - a fact that has many obstetricians on the defensive as the government strives to drive down America's relatively high rate of the costly and risky procedures.
Now, the first national study of the issue says medical conditions don't explain the variations between hospitals.
Katy Kozhimannil, a University of Minnesota professor who spearheaded the study, said that a woman should get the same treatment regardless of where she goes to deliver her baby. But that's clearly not the case, she said.
"Her likelihood of having a cesarean varied between 11 percent and 36 percent across hospitals â ¦ regardless of her diagnosis," Kozhimannil said.
The variation across hospitals exists for women both at high-risk for C-section deliveries and for those at low-risk, she said. "And so that means that we're not getting the right cesareans to the right women."
The study, published in PLOS Medicine, analyzed data from nearly 1.5 million live births at 1,373 U.S. hospitals from 2009 and 2010.
The data, from the Healthcare Cost and Utilization Project's Nationwide Inpatient Sample, is a representative sample of a fifth of all U.S. hospitals.
But shortcomings in the data meant that Kozhimannil and her co-authors at the Harvard School of Public Health in Boston were unable to pinpoint what accounts for the variations in hospital C-section rates.
They analyzed patients with diabetes, hypertension, hemorrhages, placental complications, fetal distress, fetal disproportion and obstructed labor. They considered maternal age, race and ethnicity, insurance status, hospital size, location and teaching status.
But the data lacked key information about whether the women had given birth before, or gestational age at the time of delivery. As a result, it's possible that the variability between hospitals could be exaggerated, the study notes. Kozhimannil said the database also lacks information about hospital policies and practices that might affect the type of care women get.
"We can't answer the million-dollar question, which is: What is causing this variability?" she said.
Even so, after analyzing so many medical and demographic factors to satisfy the study's critical reviewers, Kozhimannil said she's nearly certain the answers won't be found in the medical conditions of the mother or the fetus.
"I think we need to do what's more uncomfortable, which is look at the broader health care system and see how it's serving women, families and clinicians," Kozhimannil said. "Maternal mortality rates have doubled since the mid-'80s. We are going in the wrong direction, and this is why I think a broader systems level look is so important."
C-sections pay about 50 percent more than vaginal births for both facilities and providers. While that's not likely to play a role in the decisions of individual doctors, it might have an influence on policies at the broader systems level, Kozhimannil said.
"There needs to be clear, evidence-based protocols â ¦ so that providers and clinicians have good guidance about how to treat people with particular clinical conditions," Kozhimannil said. "Women who are clinically the same should have similar clinical care."
Dr. Gordon C.S. Smith, professor and head of the Department of Obstetrics and Gynaecology at Cambridge University, wrote a perspective piece that accompanies Kozhimannil's report in PLOS Medicine.
He lamented the fact that the analysis lacked certain basic information, such as whether it was a woman's first birth or gestational age.
"This limits our ability to understand from this analysis why the rates varied so much and how the variation might be addressed," Smith wrote. "The weaknesses in routine collection of maternity data in the U.S. are well recognized. Why is the collection of high quality maternity data such a low priority?"
Understanding what contributes to C-section variations and identifying appropriate responses can only be done if good quality data are gathered and made available to researchers, Smith wrote.
About 1.3 million C-sections are performed annually, making it the most common inpatient surgery in the U.S. C-section rates increased annually from 20.7 percent in 1996 to 32.9 percent in 2009, when they leveled off.
The study notes that C-sections increase a woman's risk of infection, pain, re-hospitalization, breast-feeding challenges and future pregnancy complications, and that infants born this way have higher rates of hospitalization and breathing issues.
Kozhimannil said prior studies show that the primary reason cited for C-sections is something called "non-reassuring fetal status." She said doctors make the call based on readings from a fetal monitor during labor.
"It's subjective," Kozhimannil said. "That diagnosis has been used much more over time consistent with cesarean delivery," she said. "But it's less likely that it's happening for reasons where it was absolutely medically necessary because we're not seeing the same kind of increase in child survival or decrease in infant mortality (rates)."