Ultrasound Assessment of Foetal Head-Perineum Distance Prior to Induction of Labour as a Predictor of Successful Vaginal Delivery.

Background: In modern obstetrical practice, incidence of induction of labour is on rise for varied maternal and foetal indications. Ultrasound can help obstetricians in counselling patients before induction of labour and explain the probability of successful induction.

Objectives: To study the role of foetal head-perineum distance in predicting successful vaginal delivery and to correlate with other parameters such as cervical length and Bishop score.

Design: This study is a prospective case-control study in a tertiary care teaching hospital.

Population: There were 250 term patients between 37 and 40+ weeks with singleton cephalic presentation with no contraindications for vaginal delivery.

Methods: Prior to induction of labour, transperineal ultrasound was performed to measure foetal head-perineum distance. Simultaneously, cervical length was performed using transvaginal ultrasound probe. Bishop score was determined at the same time by clinical examination.

Main Outcome Measures: Outcome of induction was considered successful when it resulted in vaginal delivery. It was considered to be a failure if patient did not get into active phase of labour or an operative intervention had to be performed because of non-progress of labour in active phase of labour. Cases were excluded if caesarean delivery had to be performed in the event of foetal distress.

Results: It was observed that as the transperineal foetal head-perineum distance decreased, the rate of vaginal delivery increased. Similarly, when foetal head-perineum distance increased, the rate of caesarean delivery increased. At a cut-off ≤ 5.5 cm, foetal head-perineum distance had a maximum predictability (sensitivity 97%, specificity 88.1%).

Conclusion: Transperineal foetal head-distance measured by ultrasound can be used as an important tool to predict vaginal delivery before induction of labour.