Between 1965 and 2009, births by Caesarean section in the USA rose steadily from just a twentieth to one third of all deliveries. For 2015, the Centers for Disease Control reported 1,272,503 C-section births, now the commonest surgical procedure in US hospitals. Yet a widely cited 1985 report from the World Health Organization concluded that C-sections for medical reasons need not exceed 15%. WHO noted that certain countries whose perinatal mortality rates are among the lowest in the world have C-section rates below 10%, while adverse health consequences had been reported at frequencies above 15%.
Fortunately, presumably in response to alerts, it seems that C-section rates in the USA have recently stabilized and may even be inching down, from a peak of 32.9% in 2009 to 32.0% in 2015. But let it be noted that C-sections increase with maternal age, reaching almost half of births to women over 40.
C-sections and mortality of infants and mothers
C-sections are conducted under full anaesthesia and subject to all the risks associated with major surgery. Moreover, several reports indicate that high rates may be associated with increased mortality of babies and mothers. It is entirely understandable that women might opt for a Caesarean to benefit from advances in medical science, notably to bypass the physical challenges of vaginal birth. But mothers-to-be need reliable information on risks of the procedure to make informed decisions.
There are of course compelling reasons for delivering some babies by C-section. With obstructed labour and other obstetrical emergencies, Caesarean delivery is a life-saving procedure. So, up to a certain point, decreasing mortality for both infants and mothers should be expected to accompany increasing rates of Caesarean birth. However, beyond the threshold of medical necessity, no further decrease is likely. That is precisely what George Molina and colleagues showed in a 2015 paper. They analyzed the relationship between C-section rates and mortality of infants and mother across all 194 WHO member states. For 2012, the year considered in their analyses, the number of Caesarean births worldwide was estimated at 22.9 million, with a global C-section rate of 19.4%. Allowing for certain confounding factors such as per capita health expenditure and fertility rate, it emerged that both neonatal and maternal mortality decrease up to a C-section rate of about 19%. But a subtle difference was found with maternal mortality, which decreases rapidly up to a C-section rate of about 8% and then declines more slowly before levelling off at 19%. By contrast, infant mortality shows a single downward trend until reaching a rate of 19%.
At face value, the results presented by Molina and colleagues seemingly indicate that C-sections reduce mortality of both infants and mothers up to a rate of about 19%. This somewhat exceeds the upper limit of 15% recommended by WHO in 1985. However, the authors caution that the relationship between C-section rates and mortality may not necessarily reflect cause and effect. The average national-level figures analyzed were very coarse-grained and in many cases indirectly estimated. Moreover, confounding factors might not have been adequately excluded. For instance, provision of medical care generally increases with national income levels, so the relationship between rate of C-sections and mortality rate for infants and mothers may reflect a complex interaction with general health status of individual populations.
Side-effects of C-sections
As Molina and colleagues recognized, because Caesarean section is a surgical procedure with risks of complications, overuse may harm to both infants and mothers. Several papers report negative side-effects of C-sections for both mothers and infants. For example, in 2012 Catherine Wloch and colleagues published results of a prospective study of risk factors for surgical site infection following C-sections in 14 public hospitals in England. Overall, almost 10% of women studied developed an infection after surgery, and 0.6% were re-admitted for treatment. Being overweight emerged as a major independent risk factor for infection, with an almost fourfold increased risk for obese individuals.
Because an increasing number of women are requesting elective C-sections in the absence of medical or obstetric indications, in 2006 José Belizán and colleagues assessed risk on a broader front. Summarizing information from a review of 79 publications conducted by the National Institute for Health and Clinical Excellence in the United Kingdom (NICE), they graphically illustrated statistically significant risks of elective C-section. Most differences from vaginal birth were unfavourable, although C-section was associated with lower risks of pain in the perineal area (located between the vulva and the anus) and incontinence (reduced control over urination). Apart from those exceptions, C-sections were associated with numerous risk increase. There were relatively small increased risks for respiratory problems in the neonate and maternal mortality, but substantial increases in risks for hysterectomy, injury to the bladder plus ureters and rupture of the womb in future pregnancy.
Long-term effects of C-sections
Most discussions of harmful side-effects of C-sections focus on immediate negative impacts on infants and/or mothers. Little attention has been directed at longer-term health implications for individuals born by C-section. In fact, several studies have indicated that they often suffer more from chronic disorders related to the immune system, such as asthma, allergies and type I diabetes. Following up on these findings, Astrid Sevelsted and colleagues examined national registry data for two million Danish children born over a 35-year period (1973–2012) to explore connections between C-sections and suspected defective maturation of the immune system.
C-sections were identified as a contributory risk factor for several immunological conditions, including not only childhood maladies but also other disorders that develop later in life. Compared to children born vaginally, those born by C-section were more frequently admitted to hospital because of asthma, systemic connective tissue disorders, juvenile arthritis, inflammatory bowel disease, immune system deficiencies. leukaemia and other disorders. Overall, Sevelsted and colleagues found that the risk of developing an immune defect was about 40% greater following birth by C-section, with a 20% greater risk of developing asthma and a 10% increase for juvenile rheumatoid arthritis.
The investigators themselves emphasized that their study simply identified correlations and does not in itself demonstrate causal connections. Although their analysis was carefully designed to exclude confounding factors, it remains to be seen whether C-sections directly influence the developing immune system. It is suggestive that C-section rates and the prevalence of immune diseases—notably asthma and allergies, which have tripled in incidence over the past 50 years—have increased in parallel in industrialized nations. However, more research is needed to pin down causal influences. As a first step, it has been shown that immune system defects also occur in mice born by C-section.
High C-section rates, which have climbed to different extents around the world, are clearly a matter for concern. Huge disparities between regions surely indicate that something is amiss. George Molina and colleagues reported in their 2015 global survey that C-section rates ranged from a minimum of 0.6% in South Sudan to a startling maximum of 55.6% in Brazil. In fact, rates exceeding 90% have been reported for private clinics in Brazil and in South Africa as well. It seems that private doctors generally drive up C-section rates, triggering the expression “too posh to push” in the UK.
A 2010 survey of C-sections for dogs by Katy Evans and Vicki Adams identified a worrying precedent. Wide-headed dog breeds, such as bulldogs and Boston terriers, now have C-section rates of 80-90%. It may be too early to conclude that we could eventually end up like these pedigree dogs, but we certainly need to keep a watchful eye on increasing C-sections. In a 2016 paper introducing a “cliff-edge” model of birth mechanics, Philipp Mitteroecker and colleagues calculated that regular use of C-sections in recent decades has led to an increase of 10-20% in the incidence of mismatch between fetal and pelvic dimensions. This bodes ill for the future. However, it is encouraging that C-section rates have stabilized and may even be decreasing in the USA. We now need increased pressure from medical authorities to limit C-sections to cases of real necessity.
Belizán, J.M., Cafferata, M.L., Althabe, F. & Buekens, P. (2006) Risks of patient choice cesarean. Birth 33:167-169.
Evans, K.M. & Adams, V.J. (2010) Proportion of litters of purebred dogs born by caesarean section. Journal of Small Animal Practice 51:113-118.
Martin, J.A., Hamilton, B.E. & Osterman, M.J.K. (2015) Births in the United States, 2014. NCHS Data Brief 216:1-7.
Martin, J.A., Hamilton, B.E, Ventura, S.J., Osterman, M.J., Kirmeyer, S., Mathews, T.J. & Wilson, E.C. (2011) Births: Final data for 2009. National Vital Statistics Reports 60:1-70.
Mitteroecker, P., Huttegger, S.M., Fischer, B. & Pavlicev, M. (2016) Cliff-edge model of obstetric selection in humans. Proceedings of the National Academy of Sciences U.S.A. 113:14680-14685.
Molina, G., Weiser, T.G., Lipsitz, S.R., Esquivel, M, M., Uribe-Leitz, T., Azad, T., Shah, N., Semrau, K., Berry, W.R., Gawande, A.A. & Haynes, A.B. (2015) Relationship between cesarean delivery rate and maternal and neonatal mortality. American Journal of Obstetrics & Gynecology 314:2263-2270.
Ringgaard, A. (2014) Giant study links C-sections with chronic disorders. ScienceNordic. Retrieved from: http://sciencenordic.com/giant-study-links-c-sections-chronic-disorders
Sevelsted, A., Stokholm, J., Bønnelykke, K. & Bisgaard, H. (2015) Cesarean section and chronic immune disorders. Pediatrics 135:e92-e98.
Wloch, C., Lamagni, T., Harrington, P., Charlett, A. & Sheridan, E. (2012). Risk factors for surgical site infection following caesarean section in England: results from a multicentre cohort study. BJOG International Journal of Obstetrics & Gynaecology 119:1324-1333.
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