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Table 2 Main characteristics, results and interpretation of eight ecological studies included in the systematic review

From: What is the optimal rate of caesarean section at population level? A systematic review of ecologic studies

Study Period, data sets and source Outcomes CS range Design, Statistical method and adjustment factors Quality scoring (max = 21) Results and interpretation Considerations for socio-economic factors
Althabe et al. 2006 [12] 1991–2003 Maternal mortality 0.4–40 %) Cross-sectional 16 The association between CS and MMR and NMR is different among countries. In medium- and high-income countries, there is no association between CS and MMR and NMR; in low-income countries, as CS rates increase, maternal and neonatal mortality decease. An arbitrarily selected 10 % CS rate threshold seems to have particular implications: a system with <10 % CS rate would be unlikely to cover the medical needs. When adjusting for the considered factors (socio-economic), the observed association in low-income countries became non-significant for MMR. For NMR, the association remained but weakened. No adjustment was made for clinical factors.
119 countries grouped as low-, medium- and high-income (median 12.9 %) Linear regression models
Neonatal mortality (early) Adjustment for:
Main sources: DHS for developing countries, routine statistical surveillance systems or government reports for developed countries. Gross National Income
Proportion of skilled birth attendant
Proportion of literate population
Betrán et al. 2007 [2] 1992–2003 Maternal mortality 0.4–40.5 % (weighted average 15 %) Cross-sectional 15 In countries with high mortality, CS rate has a strong inverse association with MMR, NMR and IMR. This association weakens as mortality decreases. In low mortality countries the interpretation of the association is ambiguous. Data could support the suggestion that above a certain ceiling, higher CS rates may be associated with poorer outcomes. No adjustment was made (neither for socio-economic or clinical factors). Authors acknowledged that most likely these factors are probably important confounders and that rising CS rates possibly mirrored a change in demographic or clinical risk profile in pregnant women.
126 countries (89 % of global live births)
LOWESS plots
Neonatal mortality
Main sources: DHS for developing countries, routine statistical surveillance systems or government reports for developed countries.
Infant mortality
Jurdi et al. 2004 [19] 1995–2001 Maternal mortality 1.4–16 % Cross-sectional 15 In this group of 18 countries there is a strong inverse association between CS and MMR and IMR. This is a heterogeneous group of countries with very diverse socio-economic and health indicators. Only 3 countries had CS rates above 15 % (Lebanon 15.1 %, Qatar 15.9 %, and Bahrain 16 %). No adjustment was made (neither for socio-economic or clinical factors). But authors report, a significant positive association between CS and urban population, female literacy and Gross Domestic Product per capita.
18 Arab countries Spearman’s rank correlation (bivariate associations)
Main sources: DHS or PAPCHILD surveys, UNFPA reports. Infant mortality
McClure et al. 2007 [20] Not reported Maternal mortality Not available Cross-sectional 15 In developing countries, as CS rates increased from 0 to 10–13 %, both MMR (0–10 %) and stillbirth (0–13 %) rates decreased sharply. Above 10 % CS rate, there was no significant association. In developed countries, no relationship was found. Although this study stratifies by developed/developing countries, no further adjustment was attempted (neither for socio-economic or clinical factors).
Piecewise regression models to explore if these relationships were consistent across the entire range of values; stepwise regression identified structural breaks in the regression lines. The sample was split at the breaks and least squares regression models were created for each of the sub-samples. Correlation and linear regression analyses were conducted.
Stillbirth
188 countries grouped as developed (HDI > 0.80, n = 35) and developing n = 153)
Main sources: World Health Report 2005
Silva et al. 2010 [21] 1995–2007 (correlation for 2005) Low birth weight 22–54 %a Cross-sectional 15 LBW rate was not correlated with CS rate. However, data suggested a non-linear trend: up to a CS rate = 30 %, LBW rates tended to decline as CS increased. For CS rates >30 %, LBW rates tended to increase with CS. Data support the hypothesis that increasing use of medical interventions in more developed settings may increase LBW rates. No adjustment was made (neither for socio-economic or clinical factors).
LOWESS regression and Spearman’s rank correlation (for testing)
Brazil, 27 states
Main sources: Government database
Volpe et al. 2011 [13] 2000–2009 Maternal mortality 0.4–41.9 % (median 13.8 %) Cross-sectional 15 In countries with CS rates <15 %, higher CS rates were associated with lower MMR, NMR or IMR, and lower rates of LBW. In countries with CS rates >15 %, CS were not significantly associated with IMR or MMR (for MMR and CS, a marginally significant positive correlation was found). There was no evidence that CS > 15 % correlates to poorer, nor to better, maternal or child mortality rate outcomes. No adjustment was made (neither for socio-economic or clinical factors).
193 countries
Neonatal mortality
Main sources: DHS for developing countries, routine statistical surveillance systems or government reports for developed countries. Infant mortality Non-linear exponential models were compared to quadratic models to regress IMR, NMR, MMR and LBWR rates to CS rate. The goodness-of-fit of models was compared using Akaike’s Information Criteria (AIC).
Low birth weight
Ye et al. 2014 [4] 1980–2010 Maternal mortality CS range first year: 6.2–23 % Longitudinal analysis 18 Most of the countries have experienced sharp increases in CS rates. Once CS rate reached 10 %, with adjustment for HDI and GDP, further increases in CS rate had no impact on MMR, NMR or IMR. Country-level CS rates above 10–15 % are hardly justified from the medical perspective. Unadjusted analysis showed decline in mortality rates with increasing CS rates (up to 15 % for MMR and 20 % for NMR and IMR). After adjustment for HDI and GDP, the relationship disappeared and the curves become flat for CS rates above 10 %. The data points for CS rates <10 % were not sufficient to draw conclusions. No adjustment was made for clinical factors.
19 developed countries Two-level fractional
Main sources: routine statistical surveillance systems or government reports. Neonatal mortality CS range last year: 14.3–32.2 % polynomial model
Adjustment for:
Human Development Index (HDI)
Gross Domestic Product (GDP)
Infant mortality
Zizza et al. 2011 [14] 1994–2008 Maternal mortality 0.4–42.3 % Cross-sectional 15 The analysis showed an inverse association between CS rates and MMR, and NMR for all geographical areas except for Europe. The piecewise regression provided the breakpoint beyond which an increased CS rate does not reflect an improvement in health care. The CS values for this breakpoint for NMR and MMR are 16 % and 9 %, respectively. For NMR, after 16 % there is a trend reversal; for MMR, after 9 %, it reaches a plateau. No adjustment was made (neither for socio-economic or clinical factors).
142 countries Neonatal mortality (weighted average 14.8 %) Analysis of covariance (Ancova) and piecewise regressions
Main sources: DHS for developing countries, routine statistical surveillance systems or government reports for developed countries.
  1. CS Caesarean section, MMR Maternal Mortality Rate, LBW Low birth weight, NMR Neonatal Mortality Rate, IMR Infant Mortality Rate, DHS Demographic and Health Surveys, HDI Human Development Index
  2. aEstimated from graph