Cesarean section at full dilatation in the first birth is not associated with an increased risk of subsequent miscarriage: a historical cohort study

Introduction
Cesarean section at full dilatation has been associated with an increased risk of subsequent preterm birth. We hypothesised that there may be an increased risk of miscarriage in pregnancies that follow Cesarean section at full dilatation. This study aimed to determine if a first term (≥37 weeks) cesarean section at full dilatation is associated with an increased risk of miscarriage in the next pregnancy
Materials and methods
A historical cohort study was conducted using routinely collected hospital data within the Aberdeen Maternity and Neonatal Databank (AMND). The population included were omen who had a first term birth and who had a second birth recorded within the AMND. Logistic and multinomial regression used to determine any association with miscarriage at any gestation and for early (<13 weeks gestation) and late(13 to 23+6 weeks gestation) miscarriage, with Cesarean section at full dilatation defined as the exposure. Miscarriage in the second pregnancy (spontaneous loss of intrauterine pregnancy prior to 24 weeks gestation) was the primary outcome.
Results
In total, 33452 women were included. Women who had a first Cesarean section at full dilatation were no more likely to have a miscarriage at any gestation than women with all other modes of first birth (including all vaginal births, planned CS and first stage of labour (<10cm dilated CS) [adjusted OR 0.84 (0.66 -1.08); p=0.18]. There was no association with early or late miscarriage after a CSfd, though the sample size for late miscarriage was small.
Conclusions
This is the first observational study to investigate the risk of miscarriage following first term CSfd. We found no association between miscarriage at any gestation following a first term CSfd compared to all other modes of first birth.