Background Repeat caesarean section (CS) following previous CS is one of the most significant factors contributing to increasing CS rates globally. Even though trial or labour (TOL) is the recommended option associated with better outcomes for both mothers and babies, TOL rates vary widely through healthcare settings and countries. The aim of this study was to compare the risk of neonatal and infant mortality in women with one previous CS undergoing a subsequent TOL or elective repeat CS.

Setting Denmark (1982–2010). The Danish Civil Registration System (CRS) data were used for the current analysis. This is population-based, high-quality, validated data collected continuously on the entire population of Denmark using a unique identifer. Data were obtained from the Medical Birth Register and the National Hospital Register. Women with their first two deliveries between 1982 and 2010 (n = 550,273) were included in the study. The odds of neonatal death (<28 days) and infant death (<365 days) according to mode of delivery were compared. Women with one previous CS and subsequent elective repeat CS formed the reference group. These women were compared to women with one previous CS and a subsequent TOL. Multiple logistic regression adjusting for key potential confounders including maternal age, body mass index, smoking and history of pregnancy loss were used to compute the odds ratio (OR) and 95% confidence intervals (CI).

Results Women with one previous CS undergoing a subsequent TOL had a 68% increased odds of neonatal death (OR 1.68, 95% CI 1.05, 2.68) compared to women having an elective repeat CS in the crude analyses. This remained unchanged in the adjusted analyses (OR 1.68, 95% CI 1.05, 2.69). However, in the later years this increased risk disappeared suggesting a cohort effect (OR 1.15, 95% CI 0.69, 1.91). No increased odds of infant death was found among women with a first CS udergoing a subsequent TOL in the crude (OR 1.08, 95% CI 0.80, 1.45) and adjusted analyses (OR 0.89, 95% CI 0.63, 1.27).

Conclusion In the largest study to date we found that women with a first CS and subsequent TOL had a 68% increased odds of neonatal death compared to women with an elective repeat CS. However, this increased odds disappeared in the later years of the cohort, suggesting a cohort effect and the possibility that CS is now a much safer operation and the increased risk in the earlier years of the cohort could be due to underlying medical complications requiring a CS rather than as a result of the CS per se. This information will help expectant parents and healthcare providers to make a more informed decision regarding the optimal mode of delivery in women with one previous CS.