Objective To compare the maternal and neonatal morbidity associated with alternative instruments used to perform a mid-cavity rotational delivery.Design A prospective cohort study.Setting Two university teaching hospitals in Scotland and England.Population Three hundred and eighty-one nulliparous women who had a mid-cavity rotational operative vaginal delivery.Methods A data collection sheet was completed by the research team following delivery.Main outcome measures Postpartum haemorrhage, thirdand fourth-degree perineal tears, low cord pH, neonatal trauma, and failed or sequential operative vaginal delivery.Results One hundred and sixty-three women (42.8%) underwent manual rotation followed by non-rotational forceps delivery, 73 (19.1%) had a rotational vacuum delivery, and 145 (38.1%) delivered with the assistance of rotational (Kielland) forceps. The rates of postpartum haemorrhage were similar when comparing manual rotation with rotational vacuum (adjusted OR 1.42, 95% CI 0.66-3.98), and when comparing manual rotation with Kielland forceps (adjusted OR 1.22, 95% CI 0.71-2.88). The results were comparable for third-and fourth-degree perineal tears (adjusted OR 0.85, 95% CI 0.13-1.89; adjusted OR 0.94, 95% CI 0.39-1.82), low cord pH (adjusted OR 1.76, 95% CI 0.44-6.91; adjusted OR 1.12, 95% CI 0.44-2.83), neonatal trauma (adjusted OR 0.50, 95% CI 0.16-1.55; adjusted OR 3.25, 95% CI 0.65-16.17), and admission to the neonatal intensive care unit (adjusted OR 1.47, 95% CI 0.45-4.81; adjusted OR 1.04, 95% CI 0.49-2.19). The sequential use of instruments was less likely with manual rotation and forceps than with rotational vacuum delivery (0.6 versus 36.9%, OR 0.01, 95% CI 0.002-0.090).Conclusions Maternal and perinatal outcomes are comparable with Kielland forceps, vacuum extraction, and manual rotation, with few serious adverse outcomes. With appropriate training mid-cavity rotational delivery can be practiced safely, including the use of Kielland forceps.Keywords Mid-cavity, morbidity, operative vaginal delivery, prospective cohort study, rotational.Please cite this paper as: Bahl R, Van de Venne M, Macleod M, Strachan B, Murphy DJ. Maternal and neonatal morbidity in relation to the instrument used for mid-cavity rotational operative vaginal delivery: a prospective cohort study . BJOG 2013;120:1526-1533