The rate of Caesarean deliveries, the most common operating-room procedure performed in the United States, varies drastically among hospitals across the country, a new study has found, ranging from 7 percent of all births at the hospital with the lowest share of Caesarean deliveries to 70 percent at the hospital with the highest rate.
The study, published on Monday in the journal Health Affairs, was based on federal data of more than 800,000 deliveries at 593 hospitals in 2009. Conducted by researchers at the University of Minnesota in Minneapolis and the University of British Columbia in Vancouver, the study did not identify the hospitals because their names were not included in the data.
Caesarean deliveries are often performed to improve birth outcomes in high-risk pregnancies, but they can also be performed for the convenience of the mother or the doctor. The rate has increased significantly in recent years, to 33 percent of all births in 2011, up from 21 percent in 1996, the study said, citing numbers from the Centers for Disease Control and Prevention.
“Frankly I did not expect to see variations of this magnitude,” said Katy B. Kozhimannil, an assistant professor of health policy and management at the University of Minnesota School of Public Health. “It begs a closer look at how we structure and finance childbirth in the United States.”
Researchers decided to test rates for low-risk pregnancies because they expected that such deliveries would show less variation. In fact, those rates varied even more widely. For deliveries of single babies carried to term who were not breech and were born to mothers who had never had a Caesarean before, the rates varied from a low of 2 percent to a high of 36 percent.
The study relied exclusively on hospital discharge data, Professor Kozhimannil said, adding that the data were drawn from sparse administrative information that did not allow for a deeper analysis of why the rates varied so much. Clinical risks alone, like having twins or triplets — a factor that has increased in recent years — are not enough to explain the difference, the researchers found. Nor was the variation explained by hospital size, geographic location or an institution’s status as a teaching hospital.
And two other factors — women asking for Caesarean deliveries and doctors pushing them for reasons linked to liability — are also unlikely to explain the difference because they account for only a small percentage of all Caesareans.
Professor Kozhimannil said she suspected that the vast patchwork of health management techniques was driving the variation, including how patients are admitted, how their labor is managed and how hospitals and clinicians are paid for the work.