New research came out on December 1 that challenged the established assumption from the World Health Organization that a 10-15% cesarean rate was the 'sweet' spot beyond which more harm was done than good. 'Relationship Between Cesarean Delivery Rate and Maternal and Neonatal Mortality' made some big news and Lamaze International shared the organization's response here. Study co-author Neel Shah, MD, MPP was interviewed by Sharon Muza last week and today, author and educator Henci Goer takes a look at this new paper in comparison to other recent studies and reviews to see if they also support this newest suggestion of an appropriate cesarean rate. What do you think? What are you telling your clients, students and patients? ' Sharon Muza, Community Manager, Science & Sensibility.

A new analysis challenges the World Health Organization's (WHO's) long-held dictum that population-level cesarean rates should not exceed 10-15% because no further reductions are seen in maternal or neonatal mortality. Based on an analysis of cesarean rates in 194 countries, Molina et al. (2015) concluded that this threshold was actually 19%. Should we, then, discard the old WHO standard in favor of this new benchmark? To answer that question, let's look at some recent studies of the same issue and see how they compare with Molina et al.'s findings.

A Similar Study

A few months before publication of Molina et al.'s analysis, Ye et al. (2015) published an analysis of cesarean vs. mortality rates in 159 countries. It, like Molina, was an ecological study, meaning it involved comparisons and analyses of groups rather than individuals. Also like Molina, Ye and colleagues examined the relationship between cesarean rate and maternal and neonatal mortality, and they used the same definitions, that is, they defined maternal mortality as deaths from pregnancy-related causes up to 42 days postpartum and neonatal mortality as deaths before 28 days. Unlike Molina, Ye's was a longitudinal study, looking at the relationships as they changed over time within each country, whereas Molina was a cross-sectional study, taking a snapshot of the relationships at one point in time. Also unlike Molina, Ye stratified their findings by whether the countries were least, less, or more developed, and they controlled for variation in maternal health status and adequacy of the health care system within countries by using values from the Human Development Index (HDI) as a proxy. (The HDI measures average national achievements in three arenas: 'a long and healthy life; access to knowledge; and a decent standard of living' [p. 2].) Ye then plotted the relationship between cesarean rate and mortality within those stratifications, generating curves using both unadjusted data and data adjusted for the HDI.

Ye's results confirm the importance of adjusting for socioeconomic factors. For one thing, the least developed countries had much higher maternal and neonatal mortality rates than less and more developed countries with the same cesarean rate. This means that socioeconomic factors affect maternal and neonatal mortality independently of cesarean rate. For another, Ye found that adjustment for HDI greatly reduced the benefits of increasing cesarean rate compared with the unadjusted relationship, again confirming that the main factors influencing maternal and neonatal mortality are socioeconomic ones. In the adjusted model, no further benefits were seen for either maternal or neonatal mortality once the cesarean rate exceeded 10%. In fact, after this point, the maternal mortality rate slowly started to rise.

A Systematic Review

We also have Betran et al. (2015), a systematic review of ecological studies evaluating the association between cesarean rate and various measurements of maternal and neonatal morbidity and mortality. Because of heterogeneity among the eight included studies, the investigators deemed it inappropriate to pool data and perform a meta-analysis.

In the unadjusted analyses, the threshold cesarean rate beyond which no benefits were seen ranged from 9-16% for maternal, neonatal, and infant mortality. The sole study that stratified countries according to stage of development and controlled for socioeconomic status found no association between cesarean rate and maternal mortality or neonatal mortality in medium- to high-income countries (Althabe 2006). In low-income countries, after adjusting for socioeconomic factors, the relationship with maternal mortality became statistically insignificant, meaning the difference may have been due to chance, and while the relationship with neonatal mortality remained, it was weakened. A second study that stratified countries by degree of development found no association between cesarean rates and maternal mortality or stillbirth* in developed countries and no further benefit once the cesarean rate exceeded 10% in developing countries (McClure 2007). It would seem, then, that achieving a 10% cesarean rate in countries with rates lower than this is an indicator of the ability of the health care system to provide access to timely cesarean surgery and that rates higher than this have little or no impact on mortality rates.

A Study Limited to Developed Countries

A third study included in the systematic review, Ye et al. (2014), was limited to 19 developed countries. It's worthwhile to look at this study because doubtless most Science & Sensibility readers live in developed countries.

Investigators here presented results both unadjusted and adjusted according to both HDI and a calculation of personal purchasing power per capita. Cesarean rates increased linearly in relation to rising values of these indicators. Since these were all developed countries where all women had ready access to cesareans and more than 95% of laboring women had skilled birth attendants, this implies that factors other than medical necessity drove cesarean rates. And as we saw in Ye et al. (2015) and the systematic review, controlling for socioeconomic factors makes a difference. Unadjusted, the inflection point for cesarean rate and maternal mortality reduction was 15%, and neonatal and infant (deaths in the 1st year) mortality declined minimally after cesarean rates reached 20%. After adjustment, neonatal and infant mortality curves went flat after cesarean rates reached 10%, and maternal mortality declined with cesarean rate increase up to 15% and began rising again once cesarean rates exceeded 20%.

Who Wins the Duel?

What can we conclude from all this? The pattern is clear: failure to control for socioeconomic factors, as Molina did, inflates the benefits of cesarean surgery. The WHO recommendation that population-based cesarean rates should not exceed 10-15% is upheld. It hardly matters, though, since the cesarean rate in the U.S. and most other developed and developing countries is way too high whoever's standard you choose to apply.

*This surprised me because having a first cesarean is associated with an increased risk of stillbirth in the next pregnancy. I would have thought that at some point, enough babies would be exposed to the hazard that stillbirth rates would begin to rise in concert with further increase in cesarean rates.

References

Althabe, F., Sosa C., Belizan, J. M., Gibbons, L., Jacquerioz, F., Bergel, E. (2006). Cesarean section rates and maternal and neonatal mortality in low-, medium-, and high-income countries: an ecological study. Birth, 33(4), 270-277.

Betran, A. P., Torloni, M. R., Zhang, J., Ye, J., Mikolajczyk, R., Deneux-Tharaux, C., . . . Gulmezoglu, A. M. (2015). What is the optimal rate of caesarean section at population level? A systematic review of ecologic studies. Reprod Health, 12, 57. doi:10.1186/s12978-015-0043-6

McClure, E. M., Goldenbert, R. I., Bann, C. M. (2007). Maternal mortality, stillbirth and measures of obstetric care in developing and developed countries. Int J Gynaecol Obstet, 96(2), 139-146.

Molina, G., Weiser, T. G., Lipsitz, S. R., Esquivel, M. M., Uribe-Leitz, T., Azad, T., . . . Haynes, A. B. (2015). Relationship Between Cesarean Delivery Rate and Maternal and Neonatal Mortality. JAMA, 314(21), 2263-2270. doi:10.1001/jama.2015.15553

Ye, J., Betran, A. P., Guerrero Vela, M., Souza, J. P., & Zhang, J. (2014). Searching for the optimal rate of medically necessary cesarean delivery. Birth, 41(3), 237-244. doi:10.1111/birt.12104

Ye, J., Zhang, J., Mikolajczyk, R., Torloni, M. R., Gulmezoglu, A. M., & Betran, A. P. (2015). Association between rates of caesarean section and maternal and neonatal mortality in the 21st century: a worldwide population-based ecological study with longitudinal data. BJOG. doi:10.1111/1471-0528.13592

About Henci Goer

Henci Goer

Henci Goer, award-winning medical writer and internationally known speaker, is the author of The Thinking Woman's Guide to a Better Birthand Optimal Care in Childbirth: The Case for a Physiologic Approach, She is the winner of the American College of Nurse-Midwives 'Best Book of the Year' award. An independent scholar, she is an acknowledged expert on evidence-based maternity care.

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