The relationship between cesarean delivery and fecundability: a population-based cohort study

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BackgroundPrevious studies have found that women with caesarean delivery have fewer pregnancies. Caesarean delivery is also more common among women with lower fecundability. The potential role of caesarean delivery on reduced fecundability is not known. ObjectiveTo assess the bidirectional relationship between caesarean delivery and fecundability. Study DesignThis is a prospective cohort study based on data from the Norwegian Mother, Father, and Child Cohort study linked with the Medical Birth Registry of Norway. We estimated the fecundability ratio (per cycle probability of pregnancy) and relative risk of infertility (time to pregnancy ≥ 12 months) according to mode of delivery in the previous delivery among 42,379 women. For the reverse association, we estimated the relative risk of having a caesarean delivery by fecundability (the number of cycles women needed to conceive) among 74,025 women. ResultsThe proportion of women with infertility was 6.2% (2711/43936) among women with prior vaginal delivery, and 8.6% (518/6036) among women with a prior caesarean delivery, yielding an adjusted relative risk of 1.21 (95% confidence interval: 1.10 to 1.33). Women with previous caesarean delivery also had lower fecundability ratio (0.90, 95% confidence interval 0.88 to 0.93), compared to women with prior vaginal delivery. When assessing the reverse association between fecundability and caesarean delivery, we found that women who did not conceive within 12 or more cycles had higher risk of caesarean delivery (adjusted relative risk 1.55, 95% confidence interval 1.46 to 1.64) compared to women who conceived within the first two cycles. Associations remained after controlling for sociodemographic and clinical risk factors and were observed across parity groups. ConclusionAmong women with more than one child, those who had caesarean delivery had subsequent lower fecundability ratio and increased infertility risk compared to those who had vaginal delivery. However, women who needed longer time to conceive were also more prone to be delivered by caesarean delivery. We therefore found evidence of a bidirectional relationship between caesarean delivery and fecundability. This could be due to a common underlying explanatory mechanism, and the surgical procedure itself may not directly influence fecundability.