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.

OBJECTIVES: To identify risk factors and morbidity associated with suboptimal instrument placement at instrumental delivery.

DESIGN: Observational study, nested within a randomised controlled trial.

SETTING: Two university-affiliated maternity hospitals.

SAMPLE: A cohort of 478 nulliparous women at term (≥37 weeks of gestation) undergoing instrumental delivery.

METHODS: Univariable and multivariable logistic regression analyses were performed.

MAIN OUTCOME MEASURES: Risk 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.

RESULTS: Instrument 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 4 minutes longer in the suboptimal group (95% CI 2.1-5.9 minutes).

CONCLUSIONS: Suboptimal 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.