Fetal umbilical artery flow velocity waveforms: prediction of small for gestational age infants and late decelerations in labour.

The relationship between fetal umbilical artery waveform patterns and (a) small for gestational age infants or (b) late fetal heart rate (FHR) decelerations in labour was examined in 205 clinically high-risk pregnancies. All pregnancies were studied using continuous-wave Doppler Ultrasound within 7 days of delivery. Waveforms were analysed by calculating a ratio of peak systolic frequency to end diastolic frequency (A/B ratio). An abnormal Doppler result was defined as being above the 97th centile for gestation from our previously derived normal values. Abnormal Doppler results occurred in only 38% of small for gestational age (SGA) infants and in 70% of those developing late decelerations in labour. Doppler ultrasound is a poor predictor of SGA infants, but may identify a high proportion of cases at risk of developing late FHR decelerations in labour.