AbstractIntroductionDelivery by vacuum extraction is a major risk factor for obstetric anal sphincter injury. The aim of this study was to assess risk factors for obstetric anal sphincter injury in vacuum extraction in nulliparous women, specifically operator‐related factors. A secondary aim was to assess other complications of vacuum extraction that are dependent on operator experience.Material and methodsA historical cohort study of nulliparous women with a live single fetus ≥34 weeks, delivered by vacuum extraction at a teaching hospital in Sweden in 1 year (2013), using data from medical records. Risk of obstetric anal sphincter injury was assessed for obstetricians (reference), gynecologists, and residents, and adjusted for maternal, fetal, procedure‐related, and operator‐related covariates using unconditional logistic regression. Results are presented as prevalence and crude and adjusted odds ratio (aOR) with 95% CI.ResultsIn total, 323 nulliparous women delivered by vacuum extraction were included. Obstetric anal sphincter injury occurred in 57 (17.6%) women. Fifteen (11.5%) obstetric anal sphincter injuries occurred in vacuum extractions performed by obstetricians, 10 (13.5%) by gynecologists (aOR 1.84, 95% CI 0.72‐4.70), and 32 (26.9%) by residents (aOR 5.13, 95% CI 2.20‐11.95). Maternal height ≤155 cm (aOR 4.63, 95% CI 1.35‐15.9) and conversion to forceps (aOR 19.4, 95% CI 1.50‐252) increased the risk of obstetric anal sphincter injury. Operator gender, night shift work, or being a frequent operator did not affect the risk of obstetric anal sphincter injury. Postpartum hemorrhage and fetal complications did not differ between operator categories.ConclusionsThe adjusted risk of obstetric anal sphincter injury in nulliparous women was five times higher in vacuum extractions performed by residents compared with those performed by obstetricians. Vacuum extractions performed by gynecologists did not carry an increased risk of obstetric anal sphincter injury. Experience in years of training, rather than frequency of the procedure, seemed to have the highest impact on reducing obstetric anal sphincter injury in vacuum extractions, which indicates a need for increased training and supervision.