January 23, 2018

expert reaction to review paper looking at long-term risks and benefits of caesarean sections

Researchers, in a systematic review and meta-analysis published in PLOS Medicine, examine and analyse the long-term risks and benefits associated with caesarean delivery for mother, baby and subsequent pregnancies.

Prof. Susan Wray, Harris-Wellbeing Centre for Preterm Research, University of Liverpool, said:

“This is a well conducted literature review.  The conclusions drawn can only be as good as the number of good studies in the literature, and as the authors found, there is only one randomised control study.  Notwithstanding this I think the conclusions from this study are timely and important.  As the authors note, there was a need to assess the long term risks and benefits of C-sections, and to include both maternal and neonatal outcomes and subsequent pregnancies.

“This information will be useful to both women and those involved in their care, especially when contemplating a C-section for non-medical reasons.  Knowing there are increased risks associated with a C-section of miscarriage and still birth for future pregnancies, even though the increased risks are very small, may weigh more heavily for some women than the associated benefits of decreased risk of prolapse and urinary incontinence, and vice versa.  If the study results translate to causation rather than association then the authors show that for every 1,500 C-sections there could be an additional 187 women with subsequent sub-fertility and 1 future stillbirth (the associated risk is with future pregnancies, not with the baby being delivered by caesarean).”

Dr Rachel Tribe, Reader of Women’s Health, King’s College London, said:

“This systematic review and meta-analysis is a very useful contribution to our understanding of the ‘pros and cons’ of elective caesarean section.  It provides a solid evidence to inform clinicians and parents about the potential impact on longer term health of babies born by caesarean section.  This will be particularly useful for those considering an elective caesarean section.  Whilst the paper couldn’t directly address the reasons why babies born by caesarean section have higher rate of obesity and asthma/allergy, it is worth noting that there is growing evidence that caesareans can influence the infant gut microbiome and immune system development.

“This is a high quality meta-analysis of existing evidence and provides a comprehensive review and summary of the data from several studies.  The pre-data analysis protocol was published and changes to analysis plan were described and justified in the manuscript.  The review has included sensible studies.

“Many of the studies included adjusted for confounders such as BMI, parity and maternal age and the authors highlight that they were unable to separate out the impact of elective versus emergency caesarean.  Elective caesarean section in previously published studies has been identified as an important variable; both mother and fetus appear to benefit if labour is experienced.

“I am not sure whether any correction was made for gestation at delivery.  The authors did limit their analysis to only include births > 37 weeks, but this is still a 5 week window (37-42 weeks) and physiological exposures during this time may be different and unaccounted for e.g. different exposure to increasing concentrations of placental hormones or surfactant proteins, which could be important for fetal maturation.  I am not sure whether the impact of infant feeding was factored in.  Women delivering by caesarean have lower rates of breast feeding and breast feeding can impact on allergy/asthma and obesity risk in later life.  This would be a confounder.

“This paper provides important and useful evidence to inform decision making with regard elective caesarean section.  Both clinicians and women will benefit from more fully understanding the risks and benefits of elective caesareans.  In terms of emergency caesarean section – women informed of the potential outcomes for their babies could be better prepared to consider need for breastfeeding, nutritional interventions and promotion of healthy diet and exercise for their children if they are at increased risk of allergy/asthma and obesity.

“There are pros and cons of both vaginal delivery and caesareans.  There are some benefits to the mother by undertaking caesarean (reduced urinary incontinence and pelvic organ prolapse), but these may be outweighed by the other negative aspects – subfertility, pregnancy risks such as placenta previa, uterine rupture etc.  Also the impact on the babies’ future health is an important consideration when making a decision about elective caesareans.  Emergency caesareans cannot be avoided but for elective caesareans, women can weigh up the pros and cons and decide which aspects are most important to them.”

Prof. Andrew Shennan, Professor of Obstetrics, King’s College London, said:

“This is an important review from a credible group demonstrating significant potential harms related to future pregnancies associated with caeserean sections, with some benefits related to the mothers’ pelvic floor and bladder.  The outcomes have a plausible mechanism which suggests causation in spite of the observational nature of most of the studies informing this review.

“With an increasing trend for soft indications for caesarean sections, this will help inform both women and clinicians in deciding best management.  Risks to future pregnancies were potentially serious, including an increase in miscarriages and stillbirths, so mothers may accept small risks to herself to reduce these risks to her potential future babies by avoiding unnecessary Caesarean sections.

“Stillbirths are rare – if the association is proved to be causal, this review suggests that if all pregnant women gave birth by caesarean section, for every six stillbirths that happen anyway there would be one more due to the association with caesarean in a previous pregnancy.  For miscarriages, if the association identified here was proved to be causal, if all women were to give birth by caesarean section then for every eight miscarriages that happen anyway there would be one more due to the association with previous caesarean.”

Dr Graham Wheeler, Medical Statistician, UCL, said:

“There are several limitations with parts of this work.  Some of these analyses raise more questions than answers.

“The authors only present relative differences when comparing the risks and benefits of caesarean and vaginal delivery.  To get a clearer picture we would want an estimate of the absolute risk of these events occurring under each delivery method.

“The combined results from six studies reported a 59% increase in the odds of a child under 5 years old being obese when delivered by caesarean compared to vaginal delivery.  However, there are likely to be other underlying factors that increase both the likelihood of a mother requiring a caesarean delivery and childhood obesity, for example, genetic factors or the mother’s weight at childbirth.

“Analysis of results from four studies of around 150,000 participants found a 17% increase in the odds of a subsequent pregnancy ending in miscarriage if mothers previously had caesarean delivery rather than a vaginal delivery.  It is not clear how this risk changes over multiple pregnancies, or if mothers had experienced birthing complications or miscarriages prior to the successful delivery by caesarean.

“Whilst there is a large amount of variability between the studies analysed, this review highlights areas of interest for future research that will hopefully identify key factors affecting maternal and child health.

“The studies in this research, taken from across the world, look at a range of outcomes relating to the health of both mothers and babies delivered over the last 50 years.  Each analysis used between 9,000 and 11 million participants.

“Researchers found a 44% decrease in the odds of urinary incontinence when delivery was by caesarean compared to vaginal delivery, based on eight observational studies.  However, the individual study results were highly variable and were taken from different countries, across different time periods.  One clinical trial of 2088 women randomised to planned caesarean delivery or planned vaginal delivery found little evidence of this same effect.

“Though an increase in the odds of women having a miscarriage or stillbirth in subsequent pregnancies following a caesarean delivery was reported, there was little evidence to suggest an increase in the odds of perinatal or neonatal death.

“Care needs to be taken when considering the impact of caesarean deliveries on subsequent pregnancies.  For example, the chance of a mother’s second pregnancy resulting in a stillbirth may depend on whether her first baby was delivered by caesarean, but also on some confounding factor that increases both the overall chance of a stillbirth happening and the chance of a caesarean delivery being required.

“Researchers did not assess whether caesarean deliveries were planned or unplanned, which may affect the reported risks and benefits when compared to vaginal delivery.

“All studies analysed were from high-income countries in terms of GDP, so these results may differ in countries with a lower GDP.”

* ‘Long-term risks and benefits associated with cesarean delivery for mother, baby, and subsequent pregnancies: Systematic review and meta-analysis’ by Oonagh E. Keag et al. published in PLOS Medicine on Tuesday 23 January 2018.

Declared interests

Prof. Susan Wray: “I have no conflicts of interest.”

Dr Rachel Tribe: “I have a research interest in neonatal gut health following vaginal and caesarean section delivery.  I am undertaking a commercially funded study of probiotic supplementation for babies born by CS.  I have recently submitted a review for J Physiol entitled ‘Parturition and the perinatal period: can the mode of delivery impact on the future health of the neonate?’.”

Prof. Andrew Shennan: “I have no conflicts of interest.”

Dr Graham Wheeler: “I am a employed by UCL, have a visiting researcher position at the MRC Biostatistics Unit at the University of Cambridge, am a Fellow of the Royal Statistical Society, and a voluntary research committee member for Chiltern Music Therapy, a not-for-profit organisation providing music therapy services.  I have received honoraria from Novametrics Consulting Ltd.”