Attributes of Nulliparous Women Who Have a Spontaneous Vaginal Birth in Queensland: A Retrospective Cohort Study

ABSTRACT Aim This study aims to identify factors associated with spontaneous vaginal birth in nulliparous women. Material and Methods Design: Retrospective cohort study. Setting: All public and private maternity units in Queensland, Australia. Population: Nulliparous women who labour and birth a singleton baby at term from 1st January 2017–31st December 2018. Main outcome measure: Non‐instrumental spontaneous vaginal birth. Data from Perinatal Data Collection and Queensland Admitted Patient Data Collection were extracted. Participants were categorised by labour onset (spontaneous or induced). Multivariable stepwise regression models identified independent predictive factors associated with spontaneous vaginal birth. Results 37 569 participants were included. Younger maternal age compared to 40+ was associated with higher odds of spontaneous vaginal birth (spontaneous labours < 20: OR 3.723, 20–24: OR 2.545, 25–29 OR 2.062, 30–34 OR 1.522 and induced labours < 20 OR 4.345, 20–24 OR 3.031, 25–29 OR 2.031, 30–34 OR 1.641). Advanced gestation ≥ 42 weeks decreased spontaneous vaginal birth odds versus 38 weeks (spontaneous OR 0.445, induced 0.334). Breech presentation lowered SVB odds (spontaneous OR 0.067, induced OR 0.179). Absence of cardiotocography (spontaneous OR 3.444) and absence of fetal scalp lactate (spontaneous OR 3.885, induced OR 3.081) increased spontaneous vaginal birth likelihood. Women without epidurals (spontaneous OR 2.981, induced OR 2.552) were more likely to have spontaneous vaginal birth. Conclusions The characteristics with the largest magnitude of effect on spontaneous vaginal birth were similar in both spontaneous and induced labours. Interventions during spontaneous labour were associated with reduced odds of spontaneous vaginal birth.