Background
Prolonged second stage of labour is known to be associated with higher caesarean section rates. However, the association between prolonged second stage of labour (PSSL) and adverse neonatal outcomes remains contradictory. The aim of this study was to assess the association between prolonged second stage of labour and obstetric and neonatal outcomes.

Methods
This was a retrospective cohort study of women with term, singleton pregnancies at the Mater Mother’s Hospital, Brisbane. Intrapartum, maternal and neonatal outcomes were assessed and stratified according to prolonged second stage of labour.

Results
Of 48 352 women, 9.7% had PSSL. Women with PSSL were more likely to be nulliparous and have received oxytocin for augmentation of their labour (P < 0.001), less likely to have an epidural or have undergone induction of labour (P < 0.001). Women with PSSL were less likely to achieve a spontaneous vaginal delivery (adjusted odds ratio (aOR) 0.13, 95%CI 0.12–0.14, P < 0.001), more likely to undergo an instrumental delivery (aOR 3.93, 95%CI 3.62–4.25, P < 0.001) or emergency caesarean section (aOR 9.08, 95%CI 8.00–10.29, P < 0.001). PSSL was associated with shoulder dystocia (aOR 1.61, 95%CI 1.42–1.81, P < 0.001), and postpartum haemorrhage (aOR 1.37, 95%CI 1.16–1.60, P < 0.001). Univariate analysis demonstrated prolonged second stage of labour was associated with low five‐minute Apgar score, acidosis and neonatal intensive care admission. However, after adjusting for potential confounders only five‐minute Apgar scores ≤3 remained significantly increased (aOR 2.36, 95% CI 1.36–4.09, P = 0.002). Conclusion PSSL is associated with increased operative birth and maternal morbidity.