Direct standardization method according to Robson classification for comparison of cesarean rates.

Background: Compare cesarean section rates between populations or within a population over time using the crude measure is biased mainly due to differences in the characteristics of the obstetric population. The Robson Ten Group Classification (RTGC) is being widely used all over the world based on a few basic obstetrics variables.

Objectives: Propose a method of direct standardization according to RTGC to make the overall rates of cesarean sections comparable between different populations or within the same population over time.

Methods: We used data from the WHO Global Maternal and Perinatal Health Survey (WHOGS) conducted between 2004 and 2008 and data from the WHO Multinational Survey on Maternal and Neonatal Health (WHOMCS) conducted between 2010 and 2011, covering information from obstetric population of 21 countries. The standard population was based in the average size of Robson Groups in WHOMCS. The crude and standardized rates, their differences intra and inter populations, and its respective confidence intervals were calculated.

Results: The impact and importance of the method were demonstrated. The five leading countries list on cesarean rates was completely modified and changes of cesarean rates over time in the same country varied in both directions by the standardization.

Conclusion: This method is useful to compare overall rates as an additional information when RTGC Report Table is been used or, for some type of studies as analytical ecologic studies with multiple groups, where leading with the report tables are laborious and hard to interpret. The use of Robson Ten Group Classification for direct standardization of cesarean rates is easy to apply and interpret.