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.