Doppler Technology

In combination, Doppler assessment of these four vessels—the maternal uterine arteries, the fetal umbilical arteries, the MCA, and the DV—is key to evaluating maternal responses, placental responses, and fetal responses to altered resistance and subsequent intrauterine growth restriction (IUGR). It also can guide us in the timing of intervention for IUGR, mainly in decisions about when the baby should be delivered and when we should wait a few more days. In a critical sense, then, Doppler is useful in managing the pregnancy.

Doppler can be useful in several other specific instances as well. When assessing and monitoring a fetus for a heart problem—sustained tachycardia, for instance—a look at the DV can be key to understanding the effects of medication given to the mother to alter the fetal heart rate.

Doppler evaluation of the MCA, on the other hand, can be used to assess the anemic fetus. Thin blood moves rapidly, and the absolute velocity of blood flow through the MCA can be analyzed with confidence and used to assess the likelihood that the fetus has anemia—as sometimes occurs with Rh disease, maternal infection, or trauma, for instance—and whether the fetus needs intrauterine transfusions.

Screening Potential

In the regular ob.gyn. practice, then, Doppler ultrasound can certainly be employed in cases of inadequate fetal growth and in cases in which we want to know directly how the placenta is doing—in a patient who had a previous stillbirth or previous IUGR baby, for instance, or in patients for whom we have reason to suspect fetal anemia.

We can extrapolate this further, and ask whether there is a role for Doppler screening. Should everyone receive a Doppler evaluation to detect IUGR and other problems?

A significant amount of research has been done, and is ongoing, to determine Doppler's screening roles. In this context, it is important to consider individual vessels separately. There probably is no role for screening with MCA Doppler (

Ductus venosus Doppler can easily be done, in fact, in the context of the first-trimester ultrasound examination. In a study we recently completed at the University of Maryland, abnormal first-trimester DV Doppler findings were predictive of adverse outcomes—including cardiovascular defects, fetal growth restriction, and aneuploidy—in fetuses with normal nuchal translucency. (See

(Doppler assessment had been known previously to increase the predictive accuracy for Down syndrome when NT is increased. In this study we looked at cases with normal NT.) With respect to the uterine artery and umbilical artery, Doppler's screening applications (in the first half of pregnancy) is not as reliable as its diagnostic role. Patients showing abnormal placental blood-flow resistance before 20–22 weeks may still show normal blood -low patterns in the third trimester, with a normal mother and normal fetus, so we should not base major clinical management decisions or therapies on early Doppler screening.

Although there is not perfect correlation, there does appear to be potential value in Doppler screening in the first half of pregnancy. Uterine artery screening has been used in the first and second trimesters to detect cases in which placental development is deficient enough to put mothers at high risk for developing preeclampsia or isolated hypertension, and it turns out that elevated resistance and persistent notching are significantly predictive of the onset—and even, in some trials, the severity—of hypertensive complications.

Evidence has also suggested that detection of these abnormalities at 11–12 weeks, followed by the administration of low-dose aspirin (ranging in trials from 81 mg to 120 mg daily), may be effective in reducing the incidence of hypertension and preeclampsia.

Although larger trials are underway, they have not yet substantiated the benefits of low-dose aspirin that were seen in the small, original trials; nevertheless, at this point the potential of reducing the incidence and severity of hypertensive complications makes Doppler screening a worthwhile consideration.

Ultimately, I believe, trials will prove that uterine artery Doppler by itself is not the only answer for the detection of hypertensive complications, but is a valuable tool to be used in the context of other forms of evaluation—a conclusion that reflects a broader axiom of Doppler technology.

This principle may be even better illustrated when we consider umbilical artery Doppler screening. We might think that the inability of the fetus to properly develop umbilical arterial perfusion of the placenta would be virtually guaranteed to predict poor placental development and subsequent IUGR. Although that is largely true, studies have shown that it can be up to 24–28 weeks before Doppler predicts with optimal precision the likelihood of severe IUGR.