Characteristics in the first vaginal birth and their association with mode of delivery in the subsequent birth.

BACKGROUND The extent to which complications or adverse outcomes in a first vaginal birth may contribute to mode of delivery in the next birth remains unclear. This study examines the impact of the first birth on subsequent mode of delivery. METHODS The study population included women with a first vaginal birth and a consecutive second birth. Data were obtained from linked birth and hospital records for the state of New South Wales, Australia 2000-09. The primary outcome was the mode of delivery for the second birth. Planned caesarean was modelled using logistic regression; intrapartum caesarean and instrumental delivery were modelled using multinomial logistic regression. RESULTS Of the 114 287 second births, 4.2% were planned caesarean, 3.0% were intrapartum caesarean and 4.8% were instrumental deliveries. Adjusted risk factors from the first birth for a planned second birth caesarean were third to fourth degree tear [odds ratio (OR) = 5.0 [95% confidence interval (CI) 4.6, 5.4]], severe neonatal morbidity (OR = 3.2 [95% CI 2.9, 3.6]), perinatal death (OR = 3.2 [95% CI 2.3, 4.4]), severe maternal morbidity (OR = 2.8 [95% CI 2.3, 3.3]), instrumental delivery, large infant, labour induction, epidural use, use of oxytocin for augmentation and episiotomy. Important risk factors (OR > 2) for intrapartum caesarean in the second birth were perinatal death or severe neonatal morbidity in the first birth. Risk factors for instrumental delivery in the second birth were perinatal death, preterm delivery and instrumental delivery. CONCLUSIONS Obstetrical interventions and adverse pregnancy outcomes in the first birth were associated with increased risk of operative delivery in the second birth.