Screening for placental insufficiency by uterine artery Doppler

Doppler ultrasound provides a non-invasive method for the study of the uter oplacental circulation. In normal pregnancy, impedance to flow in the uteri ne arteries decreases with gestation, which may be the consequence of troph oblastic invasion of the spiral arteries and their conversion into low-resi stance vessels. Preeclampsia and intrauterine growth restriction are associ ated with failure of trophoblastic invasion of spiral arteries, and Doppler studies in these conditions have shown that impedance to flow in the uteri ne arteries is increased. A series of screening studies involving assessmen t of impedance to flow in the uterine arteries have examined the potential value of Doppler in identifying pregnancies at risk of the complications of impaired placentation. This review examines the findings of Doppler studie s in unselected populations that provided sufficient data to allow calculat ion of the performance of the test. The literature search identified 15 suc h studies, but they provided discrepant results, which may be the consequen ce of differences in Doppler technique for sampling, the definition of abno rmal flow velocity waveform, differences in the populations examined, the g estational age at which women were studied, and different criteria for the diagnosis of pre-eclampsia and intrauterine growth restriction. Nevertheles s, the studies provided evidence that increased impedance to flow in the ut erine arteries is associated with increased risk for subsequent development of pre-eclampsia, intrauterine growth restriction and perinatal death. In addition, women with normal impedance to flow in the uterine arteries const itute a group that have a low risk of developing obstetric complications re lated to uteroplacental insufficiency. It is possible that increased impeda nce identifies about 50% of pregnancies that subsequently develop preeclamp sia and about 30% of those that develop intrauterine growth restriction. Ab normal Doppler is better in predicting severe rather than mild disease. The sensitivity for severe disease requiring early delivery is about 80% for p re-eclampsia and 60% for intrauterine growth restriction.