• Sinéad M O'Neill, Ali S Khashan, Tine B Henriksen, Louise C Kenny, Patricia M Kearney, Preben B Mortensen, Richard A Greene, and Esben Agerbo.
• National Perinatal Epidemiology Centre, Department of Obstetrics and Gynaecology, Cork University Maternity Hospital, 5th Floor, Wilton, Cork, Ireland sinead.oneill@ucc.ie.
• Hum. Reprod. 2014 Nov 1; 29 (11): 2560-8.

Study QuestionDoes a primary Caesarean section influence the rate of, and time to, subsequent live birth compared with vaginal delivery?Summary AnswerCaesarean section was associated with a reduction in the rate of subsequent live birth, particularly among elective and maternal-requested Caesareans indicating maternal choice plays a role.What Is Known AlreadySeveral studies have examined the relationship between Caesarean section and subsequent birth rate with conflicting results primarily due to poor epidemiological methods.Study Design, Size, DurationThis Danish population register-based cohort study covered the period from 1982 to 2010 (N = 832 996).Participants/Materials, Setting, MethodsAll women with index live births were followed until their subsequent live birth or censored (maternal death, emigration or study end) using Cox regression models.Main Results And The Role Of ChanceIn all 577 830 (69%) women had a subsequent live birth. Women with any type of Caesarean had a reduced rate of subsequent live birth (hazard ratio [HR] 0.86, 95% confidence intervals [CI] 0.85, 0.87) compared with spontaneous vaginal delivery. This effect was consistent when analyses were stratified by type of Caesarean: emergency (HR 0.87, 95% CI 0.86, 0.88), elective (HR 0.83, 95% CI 0.82, 0.84) and maternal-requested (HR 0.61, 95% CI 0.57, 0.66) and in the extensive sub-analyses performed.Limitations, Reasons For CautionLack of biological data to measure a woman's fertility is a major limitation of the current study. Unmeasured confounding and limited availability of data (maternal BMI, smoking, access to fertility services and maternal-requested Caesarean section) as well as changes in maternity care over time may also influence the findings.Wider Implications Of The FindingsThis is the largest study to date and shows that Caesarean section is most likely not causally related to a reduction in fertility. Maternal choice to delay or avoid childbirth is the most plausible explanation. Our findings are generalizable to other middle- to high-income countries; however, cross country variations in Caesarean section rates and social or cultural differences are acknowledged.Study Funding/Competing InterestsFunding was provided by the National Perinatal Epidemiology Centre, Cork, Ireland and conducted as part of the Health Research Board PhD Scholars programme in Health Services Research (Grant No. PHD/2007/16). L.C.K. is a Science Foundation Ireland Principal Investigator (08/IN.1/B2083) and the Director of the SFI funded Centre, INFANT (12/RC/2272). The authors have no competing interests to declare.© The Author 2014. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

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