Risk factors and morbidity associated with suboptimal instrument placement at instrumental delivery: observational study nested within the Instrumental Delivery & Ultrasound randomised controlled trial ISRCTN 72230496

ObjectivesTo identify risk factors and morbidity associated with suboptimal instrument placement at instrumental delivery. DesignObservational study, nested within a randomised controlled trial. SettingTwo university-affiliated maternity hospitals. SampleA cohort of 478 nulliparous women at term (37weeks of gestation) undergoing instrumental delivery. MethodsUnivariable and multivariable logistic regression analyses were performed. Main outcome measuresRisk factors for suboptimal application of vacuum or forceps, maternal and neonatal morbidity, and the sequential use of instruments, second operator, and caesarean section following failed instrumental delivery. ResultsInstrument placement was suboptimal in 138 of 478 (28.8%) deliveries. Factors associated with suboptimal instrument placement included fetal malposition (OR 2.44, 95% CI 1.62-3.66), mid-cavity station (OR 1.68, 95% CI 1.02-2.78), and forceps as the primary instrument (OR 2.01, 95% CI 1.33-3.04). Compared with optimal instrument placement, suboptimal placement was associated with prolonged hospital stay (adjusted OR 2.28, 95% CI 1.30-4.02) and neonatal trauma (adjusted OR 4.25, 95% CI 1.85-9.72). Suboptimal placement was associated with a greater use of sequential instruments (adjusted OR 3.99, 95% CI 1.94-8.23) and caesarean section for failed instrumental delivery (adjusted OR 3.81, 95% CI 1.10-13.16). The mean decision to delivery interval (DDI) was 4minutes longer in the suboptimal group (95% CI 2.1-5.9minutes). ConclusionsSuboptimal instrument placement is associated with increased maternal and neonatal morbidity and procedural complications. Greater attention should be focused on instrument placement when training obstetricians for instrumental delivery.