The prognostic value of fetal ultrasonography before induction of labour

Abstract

OBJECTIVE: To investigate whether ultrasound examination of the fetus and amniotic fluid before induction of labour can provide useful prognostic information about the course of labour and mode of delivery. DESIGN: A prospective observational study. SETTING: The delivery suite of St Mary's Hospital, London. SUBJECTS: 101 women undergoing induction of labour. MEASURED VARIABLES: Biparietal diameter, head circumference, abdominal circumference, occipital position, amniotic fluid volume and umbilical artery Doppler velocimetry waveforms. MAIN OUTCOME MEASURES: The outcome of labour was assessed in terms of the induction delivery interval, the mode of delivery and the incidence of abnormal cardiotocograms in labour. RESULTS: Seven women were delivered by emergency caesarean section early in the first stage of labour because of a significant abnormality of the fetal heart trace and these pregnancies were characterized by small fetal abdominal circumference measurements. Marked oligohydramnios was also noted in five of these seven subjects. Small or average size babies who were surrounded by an adequate volume of amniotic fluid tended to be born spontaneously, whereas the majority of operative deliveries for failure to progress in labour were associated with fetal abdominal circumference measurements > or = 340 mm. The mean Bishop score of women before labour who delivered spontaneously was not significantly different from the scores of women who had a forceps delivery or caesarean section. Abnormal cord Doppler waveforms were observed in only one instance. CONCLUSIONS: In women undergoing induction of labour, the measurement by ultrasonography of two variables (fetal abdominal circumference and amniotic fluid volume) may allow the prospective identification of pregnancies at increased risk of fetal distress or dystocia. If these findings can be replicated in early spontaneous labour than more rational utilization of resources may be possible in hospital based obstetric practice.