Around 1.3 million Cesarean section deliveries take place in the US every year, making the procedure the most common inpatient surgery in the country. Rates of delivery by Cesarean section are known to differ across hospitals, but how much of this variation is down to women's medical conditions? A new study investigates.

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Researchers say the variation in hospital C-section rates is not explained by mothers' medical conditions, demographic status or characteristics of the hospital - such as its size or location.

Cesarean section (C-section) is a form of surgery used to deliver a baby. It involves a small incision in the mother's abdomen and uterus, from which the baby is delivered. Mothers can elect to have a C-section, or the surgery may be carried out in the event of unforeseen medical problems that may put the mother or baby at risk.

Rates of C-section soared between 1996 and 2009, from 20.7% to 32.9%, but have since leveled off. However, the research team - including Katy Kozhimannil of the University of Minnesota School of Public Health in Minneapolis - notes that there are large variations in the use of C-sections across hospitals in the US.

Identifying the reasons behind hospital variations in C-section rates may help improve the quality of health care given to mothers undergoing the procedure and their infants, the researchers say.

"Cesarean section use may vary across hospitals owing to case-mix differences, but nonclinical factors can also affect use, presenting opportunities to reduce medically unnecessary Cesarean sections," they add. "Obstetricians and other maternity care providers recognize the urgent need to address both the rising rates and variability in the likelihood of Cesarean delivery."

Variation in hospital C-section rates very high

To reach their findings, published in the journal PLOS Medicine, the researchers analyzed data of 1,475,457 births in 1,373 hospitals - representing around 20% of hospitals in the US. Data was gathered from the 2009 and 2010 Nationwide Inpatient Sample of the Health Cost and Utilization Project.

The team found that the average C-section rate among all women was 33%, while the rate among women who had not undergone the procedure previously was 22%. These rates varied by women's maternal age, race/ethnicity, insurance status and medical conditions linked to pregnancy and delivery.

When assessing the variability of C-section rates among hospitals, however, they found it was very high.

The likelihood of a C-section for all women ranged from 19-48%, varying between 11-36% for women who had not had a previous C-section.

Among low-risk women, hospital C-section rates varied between 8-32%, while rates for high-risk women varied between 56-92%.

However, after adjusting for clinical diagnoses among women - including gestational diabetes, hypertension, hemorrhage during pregnancy, fetal distress, fetal disproportion and obstructed labor - such variations in hospital C-section rates did not decline.

Furthermore, no reduction in variation was seen after adjusting for women's maternal age, race/ethnicity or insurance status. Adjusting for hospital characteristics - such as size and location - also had no effect on the variation of hospital C-section rates.

Commenting on their findings, the researchers say:

"Using data on all births that occurred in 2009 and 2010 in a nationally representative 20% sample of US hospitals, we find that variation in individual risk of Cesarean section across hospitals is not explained by differences in maternal clinical diagnoses.

Data on other aspects of individual clinical complexity (including parity and gestational age) as well as hospital factors (such as guidelines, protocols, and norms) is needed to enhance understanding of the drivers of variation in the individual likelihood of Cesarean section across US hospitals."

Study findings subject to limitations

The team notes that their findings are subject to some limitations. For example, they were unable to gather data on the reasons for C-section delivery or information on policies and obstetric care guidelines for each hospital. They say this "constrains our ability to assess the appropriateness of care or many possible administrative or clinical explanations for variations in Cesarean section rates across hospitals."

Furthermore, they point out that their study does not include clinician-level information, so they were unable to assess whether variations in C-section rates across hospitals were down to speciality differences among clinicians.

"In spite of these limitations," they add, "our analysis offers important new information on variation in the use of Cesarean sections in US hospitals by utilizing a nationally representative administrative data source."

Medical News Today recently reported on a study claiming that breech babies - those whose buttocks or feet are in place to come out first during delivery instead of their head - have a higher risk of death from vaginal delivery than C-section.