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Open Access Research article

Risk adjustment models for interhospital comparison of CS rates using Robson’s ten group classification system and other socio-demographic and clinical variables

Paola Colais1*, Maria P Fantini2, Danilo Fusco1, Elisa Carretta2, Elisa Stivanello2, Jacopo Lenzi2, Giulia Pieri2 and Carlo A Perucci3

Author Affiliations

1 Department of Epidemiology, Regional Health Service, Lazio Region, Italy

2 Department of Medicine and Public Health, University of Bologna, Bologna, Italy

3 National Agency of Regional Health Services, Italy

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BMC Pregnancy and Childbirth 2012, 12:54  doi:10.1186/1471-2393-12-54

Published: 21 June 2012

Abstract

Background

Caesarean section (CS) rate is a quality of health care indicator frequently used at national and international level. The aim of this study was to assess whether adjustment for Robson’s Ten Group Classification System (TGCS), and clinical and socio-demographic variables of the mother and the fetus is necessary for inter-hospital comparisons of CS rates.

Methods

The study population includes 64,423 deliveries in Emilia-Romagna between January 1, 2003 and December 31, 2004, classified according to theTGCS. Poisson regression was used to estimate crude and adjusted hospital relative risks of CS compared to a reference category. Analyses were carried out in the overall population and separately according to the Robson groups (groups I, II, III, IV and V–X combined). Adjusted relative risks (RR) of CS were estimated using two risk-adjustment models; the first (M1) including the TGCS group as the only adjustment factor; the second (M2) including in addition demographic and clinical confounders identified using a stepwise selection procedure. Percentage variations between crude and adjusted RRs by hospital were calculated to evaluate the confounding effect of covariates.

Results

The percentage variations from crude to adjusted RR proved to be similar in M1 and M2 model. However, stratified analyses by Robson’s classification groups showed that residual confounding for clinical and demographic variables was present in groups I (nulliparous, single, cephalic, ≥37 weeks, spontaneous labour) and III (multiparous, excluding previous CS, single, cephalic, ≥37 weeks, spontaneous labour) and IV (multiparous, excluding previous CS, single, cephalic, ≥37 weeks, induced or CS before labour) and to a minor extent in groups II (nulliparous, single, cephalic, ≥37 weeks, induced or CS before labour) and IV (multiparous, excluding previous CS, single, cephalic, ≥37 weeks, induced or CS before labour).

Conclusions

The TGCS classification is useful for inter-hospital comparison of CS section rates, but residual confounding is present in the TGCS strata.