How useful is uterine artery Doppler ultrasonography in predicting pre-eclampsia and intrauterine growth restriction?

All editorial matter in CMAJ represents the opinions of the authors and not necessarily those of the Canadian Medical Association. Pre-eclampsia and intrauterine growth restriction remain important causes of maternal and neonatal complications and death. These 2 conditions are felt to be the result of abnormal placenta formation involving abnormal trophoblast invasion of spiral arteries and a reduction in vascular resistance in the uteroplacental circulation. Although the incidence of pre-eclampsia in the general obstetric population is only 5%, there is a potential for serious adverse outcomes. Maternal complications include the HELLP syndrome (hemolytic anemia, elevated liver enzymes, low platelet count), eclampsia, coagulopathy, stroke and death. Newborns affected by intrauterine growth restriction are at increased risk for hypertension, cardiovascular disease and diabetes later in life. Accurate prediction of pre-eclampsia and intrauterine growth restriction is therefore paramount to providing appropriate antenatal surveillance and therapy in an effort to improve perinatal outcomes. The uteroplacental circulation can be assessed by means of Doppler ultrasonography of the uterine arteries. This procedure has been reported in numerous studies to be a promising technique for predicting the level of risk for preeclampsia and intrauterine growth restriction. In a normal pregnancy, impeded flow in the uterine artery decreases with increasing gestational age. Uterine artery Doppler ultrasonography may be performed via the transvaginal or transabdominal route in the first or second trimester. Uterine artery waveforms are reported to be readily obtainable in more than 95% of patients. The uterine artery is identified with the use of colour Doppler ultrasonography (Figure 1). Pulsed-wave Doppler ultrasonography is then used to obtain waveforms (Figure 2). Various indices can be calculated and assessed. In this issue of CMAJ, Cnossen and colleagues report the results of their systematic review and meta-analysis of studies in which Doppler assessment of the uterine arteries was used to predict pre-eclampsia and intrauterine growth restriction. Their review was extensive: they included 74 studies of preeclampsia and 61 of intrauterine growth restriction, with no language limitations; they evaluated the accuracy of 15 Doppler indices; and they used well-described and robust statistical methods for their analyses. One of the most widely studied Doppler indices is the pulsatility index (calculated as the peak systolic flow minus the end diastolic flow divided by the mean flow). An increased pulsatility index has been associated with an increased risk for pre-eclampsia and intrauterine growth restriction. The presence of an early diastolic notch in the waveform (Figure 3) has also been shown in several studies to be associated How useful is uterine artery Doppler ultrasonography in predicting pre-eclampsia and intrauterine growth restriction?