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Recent years have seen publication of a series of large database analyses comparing outcomes of vaginal birth with cesarean delivery. They have provided sufficient data for reviewers to conduct a systematic review and meta-analysis of long-term outcomes. The first of its kind, let’s see how they did it and what they found.
Reviewers included randomized controlled trials (1 trial) and cohort studies (79 studies) of more than 1000 participants that compared outcomes between women at term having vaginal birth with women having cesarean delivery and that had at least 1 year of follow up. They evaluated maternal outcomes, childhood outcomes, and outcomes in subsequent pregnancies, limiting them to outcomes that women would be most concerned about in the opinion of the reviewers. All studies were conducted in high income countries, and many adjusted for multiple confounding factors. Adjustment had little effect on results, however, which suggests that results in studies not making adjustments are still valid.
When outcome results were pooled for meta-analysis, numbers of participants per outcome ranged from 9000 to over 1 million with most in the tens or hundreds of thousands, giving the meta-analyses enough power to detect statistically significant differences, meaning unlikely to be due to chance, even for rare outcomes. Outcomes were reported as number needed to benefit (NNB), meaning the number of cesareans needed to prevent one instance of an adverse outcome, and number needed to harm (NNH), meaning the number of cesareans that would cause one instance of an adverse outcome.
Cesarean delivery conferred some benefits compared with vaginal birth. For women, cesarean delivery reduced urinary incontinence (NNB: 17) and pelvic organ prolapse (NNB: 24). For children, it reduced inflammatory bowel disease (up to age 35) (NNB: 1092). In subsequent pregnancy, it reduced postpartum hemorrhage (NNB: 69). Tempering these benefits, most women with urinary incontinence report only mild symptoms (Altman 2007; Fritel 2004; Goldberg 2005; Gyhagen 2013; Quiboeuf 2015; Rortveit 2003; Tahtinen 2016) and differences in prevalence according to mode of delivery converge over time (Tahtinen 2016). Furthermore, the common definition of postpartum hemorrhage at vaginal birth is estimated blood loss of 500 mL or more, and healthy women suffer no ill effects from blood loss below levels of 1000 mL or more (Begley 2010).
Cesarean delivery also caused harm. Women were less likely to have more children (NNH: 9), children were more likely to have asthma (up to age 12) (NNH: 162) and to be obese (age 6-15 yrs) (NNH 28), and cesarean delivery had many serious adverse effects on subsequent pregnancy outcomes. It increased placenta previa (the placenta covers or partially covers the opening to the womb) (NNH: 494), placenta accreta (the placenta grows into or even through the uterus) (NNH 1770), placental abruption (the placenta detaches partially or completely before the birth) (NNH: 534), uterine rupture (NNH: 538), miscarriage (NNH: 69), stillbirth (NNH: 1144), hysterectomy (NNH: 1561), and antepartum (before birth) hemorrhage (NNH: 276). Reviewers summed up the harms by saying that for every 1500 cesareans, there would be approximately 9 additional cases of childhood asthma, 166 women with subfertility, 3 women with placenta previa, 2 women with uterine rupture, 21 miscarriages, and 1 stillbirth.
In addition, while conducting their literature searches, the reviewers found studies of the relationship between mode of delivery and Type 1 diabetes in the child. Type 1 diabetes had not been specified in the review protocol, so, while not included in the main data analyses, reviewers calculated an odds ratio for the pooled data, finding that cesarean delivery increased likelihood of Type 1 diabetes by 20% (OR 1.2, 5 studies, 3.35 million participants).
All too often, the comparative risks of cesarean delivery vs. vaginal birth are framed as a “chocolate vs. vanilla” decision with balanced risks vs. benefits on either side, the 2006 NIH Consensus Conference on elective cesarean being the most notable example of this (Viswanathan 2006). It’s not true. Cesarean delivery may offer some protection against pelvic floor dysfunction, but those benefits are more than counterbalanced by a long list of serious harms, including increased pregnancy loss and stillbirth.
Altman D, Ekstrom A, Forsgren C, et al. Symptoms of anal and urinary incontinence following cesarean section or spontaneous vaginal delivery. Am J Obstet Gynecol 2007;197(5):512 e1-7.
Begley CM, Gyte GM, Murphy DJ, et al. Active versus expectant management for women in the third stage of labour. Cochrane Database Syst Rev 2010(7):CD007412.
Fritel X, Fauconnier A, Levet C, et al. Stress urinary incontinence 4 years after the first delivery: a retrospective cohort survey. Acta Obstet Gynecol Scand 2004;83(10):941-5.
Goldberg RP, Abramov Y, Botros S, et al. Delivery mode is a major environmental determinant of stress urinary incontinence: results of the Evanston-Northwestern Twin Sisters Study. Am J Obstet Gynecol 2005;193(6):2149-53.
Gyhagen M, Bullarbo M, Nielsen TF, et al. The prevalence of urinary incontinence 20 years after childbirth: a national cohort study in singleton primiparae after vaginal or caesarean delivery. BJOG 2013;120(2):144-51.
Quiboeuf E, Saurel-Cubizolles MJ, Fritel X, et al. Trends in urinary incontinence in women between 4 and 24 months postpartum in the EDEN cohort. BJOG 2016;123(7):1222-8.
Rortveit G, Daltveit AK, Hannestad YS, et al. Urinary incontinence after vaginal delivery or cesarean section. N Engl J Med 2003;348(10):900-7.
Tahtinen RM, Cartwright R, Tsui JF, et al. Long-term Impact of Mode of Delivery on Stress Urinary Incontinence and Urgency Urinary Incontinence: A Systematic Review and Meta-analysis. Eur Urol 2016;70(1):148-58.
Viswanathan M, Visco AG, Hartmann K, et al. Cesarean Delivery on Maternal Request. Evidence Report/Technology Assessment No. 133. Rockville, MD: Agency for Healthcare Research and Quality; 2006. Report No.: AHRQ Publication No. 06-E009.