Are overweight and obesity associated with increased risk of cesarean delivery in Mexico? A cross-sectional study from the National Survey of Health and Nutrition

In the last 25 years, the prevalence of obesity has doubled worldwide [1]; in Mexico, 71% of adults are overweight or obese, with higher proportions in women than in men [2]. Overweight and obesity prevalence has also risen among pregnant women in Mexico, more than doubling in the past 30 years [3], which could increase the risk of obstetric and perinatal complications, compared to women with a normal Body Mass Index (BMI) [4‐11].

Several studies have documented positive associations between overweight and/or obesity and complications during pregnancy and delivery, such as hypertensive disorders [12‐14] and gestational diabetes [15‐17]; in US populations those occur most frequently in pregnant women of Hispanic descent [18]. Increased time of labor [19‐24], dystocia, and increased risk of cesarean delivery (CD) have also been found to be associated with overweight/obesity [25‐27]. It is thus important to examine mode of delivery in the context of complications associated with obesity.

In Mexico, the overwhelming majority (94%) of women deliver in health facilities, and the proportion of deliveries via cesarean reached 45% of all births in 2012 [28]. This proportion of CD is considered high relative to the World Health Organization’s (WHO) target cesarean rate of 10–15% of all births [29]. In addition to clinical indications for CD, preferences of both women and physicians influence the use of CD, which suggests that some cesareans are performed in Mexico without following established clinical criteria [28].

The relationship of BMI and cesarean delivery had been studied previously; a meta-analysis reported a positive association between cesarean delivery and overweight, obese, and severely obese women [30]. However, studies of mode of delivery in Mexico have focused on receipt of antenatal care and socio-demographic differences [31]; we have no data about the relationship of overweight and obesity and CD.

Given the high prevalence of both overweight/obesity and CD in Mexico, this is a salient issue for women, health care providers, and the health system. The aim of this study was to determine the relationship between overweight/obesity (measured using BMI) and cesarean delivery in Mexican women. We hypothesized that overweight/obesity would be independently associated with CD in the Mexican population.

Our analytic sample included 4,570 women between 12 and 49 years old who reported a live birth between 2006 and 2012. This sample represents a population of 7,277,541 Mexican women. Overweight and obesity prevalence of women of reproductive age was 66.2% (36.4% overweight and 29.8% obese) Table 1. Overweight and obese women were more likely to be older than normal BMI women. The distribution of socioeconomic status was similar by BMI (Table 1).

Women with overweight and obesity were more likely to be multiparous compared with normal BMI (normal BMI 64%; 95% confidence interval (CI) [60–68]; overweight 76%; 95% CI [73–79]; obesity 80%; 95% CI [76–84]; p = 0.001; Table 1). Women with overweight and obesity were also more likely to report existing diabetes (overweight 2% [95% CI 1–4] and obesity 3% [95% CI 2–4] vs. normal BMI 1% [95% CI 0–1]; p = 0.013) and hypertension (normal BMI 6%; 95% CI [5–9]; overweight 7%; 95% CI [5–9] and obesity 13%; 95% CI [10–16]; p = 0.001).

No differences in the presence of any complications (collapsed any/none) during pregnancy or delivery between BMI groups were found (normal BMI 61%; 95% CI [57–64]; overweight 58%; 95% CI [54–62], obesity 61%; 95% CI [57–65]; p = 0.442). When we disaggregated complications during pregnancy we found differences by BMI in hypertension (normal BMI 13%; 95% CI [10–15]; overweight 16%; 95% CI [13–18] p < 0.05; obesity 20%; 95% CI [17–24]; p = 0.004), preeclampsia-eclampsia (normal BMI 5%; 95% CI [4–8]; overweight 9%; 95% CI [7–12]; obesity 11%; 95% CI [9–14]; p = 0.001) and gestational diabetes mellitus (normal BMI 1%; 95% CI [1, 2]; overweight 3%; 95% CI [2–4]; obesity 5%; 95% CI [4–8]; p = 0.001). Figure 2. Complications at delivery - collapsed and disaggregated - did no show differences by BMI.

Women with overweight and obesity reported a proportion of CD higher than women with normal BMI (normal 39%; 95% CI [35–43]; overweight 42%; 95% CI [38–45]; obesity 52%; 95% CI [48–57]; p = 0.001); (Fig. 3).

Results from the bivariate model including only BMI and CD segregated by parity (nulliparous vs multiparous) show a relationship between multiparous women with obesity and CD (unadjusted odds ratio = 1.91; 95% CI [1.44–2.55]; see Additional file 4).

Our multivariable logistic regression model stratified by parity (nulliparous vs multiparous) show that multiparous women with obesity had higher odds of CD compared to women with normal BMI after controlling for confonders (adjusted odds ratio (aOR) = 1.89; 95% CI [1.36–2.63]; Table 2.). The presence of complications during delivery was also associated with CD, in both nulliparous (aOR = 3.50; 95% CI [2.06–5.94]) and multiparous women (aOR = 4.01; 95% CI [3.01–5.35]). In addition, both nulliparous and multiparous women who delivered at private facilities had higher odds of CD compared with those who delivered at social security facilities (nulliparous aOR = 1.95; 95% CI [1.08–3.53]; multiparous aOR = 2.51; 95% CI [1.72–3.68].

We found that in Mexico, maternal overweight and obesity are common, as is cesarean delivery, and furthermore, that obesity is independently associated with cesarean delivery in multiparous women, controlling for sociodemographic and clinical characteristics that are associated with BMI and CD. Just over 42% of women with overweight and 52% of women with obesity had a CD, compared with 39% of women with normal BMI, and 1.89 higher odds of CD were found in multiparous women with obesity when compared with normal BMI women, controlling for socio-demographic and health factors. Our results support our hypothesis that in Mexico, high BMI (obesity) is independently associated with CD, controlling for socio-demographic and health characteristics.

Overall, the proportion of deliveries via CD in our study was 44%, which supports previous evidence in Mexico [28], and is comparable with CD rates in Brazil (45.9%), the Dominican Republic (41.9%) and Cuba (35.6%) [34], positioning Latin America and the Caribbean region with the highest CD rates worldwide [35, 36]. A recent study reported better maternal and neonatal outcomes when CD rates do not exceed 19% of all births [37]; the proportion of CD found in our study is three times higher than the WHO recommendation of CD [29].

Studies in Latin American countries have reported that high CD rates were positively associated with severe maternal morbidity and mortality and higher fetal mortality rates [38]. Furthermore, increases in CD rates is not associated with improvements in other perinatal outcomes [39]. Results from a meta-analysis including cohort studies of pregnant women with anthropometric measurements shows higher odds of cesarean in women with obesity, consistent with our results [40]. A Canadian study that compared maternal outcomes between women with normal BMI and extreme obesity also found a positive association between extreme obesity and CD [41].

Studies in nulliparous women have reported a positive relationship between a high BMI (overweight and obesity) and CD [42‐44], which we did not find in our study. However, a study focused on the risk of caesarean section in obese women analysed by parity reported highest CD rates in multiparous women associated with a high rate of repeat elective CD [45]. This finding could be related to a policy of scheduling pre-labour CD for all women with one previous scar without attempting a trial of labour [46].

We found women with any self-reported complications at delivery had higher adjusted odds of CD compared with women who did not report any complications.

The same positive association between high BMI and cesarean was found in multiparous women without complications, as reported in previous studies [47].

Pre-pregnancy BMI has been studied previously in Mexico, focused on pregnancy, fetal and neonatal complications as the primary outcome [48‐50]. This previous literature has not focused on mode of delivery as an outcome. Our study fills a gap in the literature, especially given the concurrent epidemics of obesity and CD in Mexico. Although overweight and obesity are not defined as a CD indication in clinical practice guidelines [51], our results shows a strong and independent association between high BMI and CD in multiparous women. Our findings suggest that the high CD rate and obesity epidemic are linked. Health care providers should consider BMI as important factor in maternal interventions to reduce negative maternal and perinatal outcomes [47, 52].

The Mexican Health System has recognized the importance of reducing cesareans and has created official standards, technical guidelines and clinical practice guidelines to regulate and reduce the CD rate [51]. Despite these efforts, implementation of these recommendations has faced challenges and high rates persist as reported here and previously [53‐55]. Contributing factors may be the lack of training of health professionals, resistance to change and maintenance of practices not based on evidence, a perception of CD as harmless, quick and effective by pregnant women and physicians [56, 57]. Increased demand of CD by women from poor families, following trends documented in rich people, have also been reported [52].

The most important limitation of study is the timing of BMI measurement; we do not have pre-pregnancy BMI measurements, rather we have BMI measurments following delivery, at the time of survey. However, we use a large nationally representative sample with anthropometric BMI measurement (not self-report, which was previously reported to have an important bias, particularly in women [58, 59]). We explored potential bias introduced by time elapsed between delivery and survey through stratified analyses (Additional files 2 & 3) and results were robust. We provide the first population-level assessment of BMI and CD in Mexico. Our outcome and covariates (except our exposure, BMI) are self-report, which could potentially affect our results so we performed multiple sensitivity analyses with variables sensitive to recall bias (such as complications during delivery) to ensure our results were robust to model specification. Our study included only those women with complete anthropometric data, and women excluded were more vulnerable than those with complete data. The missing variables in the women excluded from the study sample corresponded to those of self-report related to sociodemographic characteristics and health history (Additional file 1). There was no lack of data in the BMI exposure variable and the type of delivery outcome. When analyzing the differences between women included and excluded from the study sample, no differences were found in the BMI exposure variable and the type of delivery outcome. Women with missing data could be those with greater vulnerability, which could limit the generalization of study results. Future studies should consider exploring in depth if these differences could be affecting the health outcome in the most vulnerable women.

The results of our study provide evidence in the Mexican population of the relationship between high BMI and risk of CD. Our results further offer new evidence about the proportion of women with overweight and obesity who deliver in Mexico, which can be used to inform maternal health programs. Given the high prevalence of both obesity and CD in Mexico, this relationship is salient for women, health care providers, and the health system. Efforts to reduce the CD rate need to take the obesity epidemic into account.