Having a Caesarean section at full dilatation (CSfd) has been associated with an increased subsequent risk of spontaneous preterm birth (sPTB). The Aberdeen Maternity and Neonatal Databank (AMND) provides a rare opportunity to study subsequent pregnancy outcomes after a previous CSfd over 40 years with an ability to include a detailed evaluation of potential confounding factors.
To investigate if having an initial CSfd is associated with sPTB or other adverse pregnancy outcomes in the subsequent pregnancy.
A retrospective cohort study was conducted including women with a first and second pregnancy recorded within the AMND between 1976 and 2017, where previous CSfd at term in the first birth was the exposure. The primary outcome was spontaneous preterm birth (defined as spontaneous birth <37 weeks). Multivariate logistic regression was used to investigate any association between CSfd and the odds of spontaneous preterm birth (sPTB). Women with a prior CSfd were compared to (a) women with any other mode of birth (b) individual modes of birth including planned CS, CS in first stage of labour (<10cm dilated), vaginal birth (including spontaneous vaginal birth (SVB), non-rotational forceps, Kielland's forceps, vacuum-assisted birth, breech vaginal birth). Other outcomes such as antepartum haemorrhage and mode of second birth were also compared.
Of the 30253 women included, 900 women had a prior CSfd in the first pregnancy. Women with prior CSfd had a three-fold increased risk of spontaneous preterm birth in a second pregnancy (unadjusted OR 2.63; 95%CI 1.82 – 3.81); adjusted OR 3.31; 95%CI 2.17 – 5.05) compared to all other modes of first birth adjusted for maternal age, diabetes, BMI, smoking, pre-eclampsia, antepartum haemorrhage, socioeconomic deprivation (SIMD 2016), year of birth and interpregnancy interval (in second pregnancy). When compared to women with vaginal births only, women with CSfd had five-fold increased odds of sPTB (aOR 5.37 (95%CI 3.40 – 8.48)). Compared to first spontaneous vaginal birth (SVB), first instrumental births (non-rotational forceps, Kielland’s forceps and vacuum births) were not associated with an increased risk of sPTB in the second birth. After an initial CSfd, 3.7% of women had a repeat CSfd and 48% had a planned CS in the second birth.
This study is a substantial addition to the body of evidence on the risk of subsequent sPTB after CSfd and demonstrates a strong association with spontaneous preterm birth following a CSfd in the first birth though the absolute risk remains small. This is a large retrospective cohort and includes a comprehensive assessment of potential confounding factors, including pre-eclampsia, antepartum haemorrhage (APH) as well as length of first and second stage of labour Future research must focus on understanding possible causality and to develop primary and secondary preventative measures.

Copyright © 2023. Published by Elsevier Inc.