The MCA Doppler and its Role in the Evaluation of Fetal Anemia and Fetal Growth Restriction

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Diagnosis of fetal anemia before the use of the middle cerebral artery peak systolic velocity

Before the widespread use of the middle cerebral artery (MCA) peak systolic velocity (PSV), the management of maternal red cell alloimmunization was based on an indirect measurement of fetal hemolysis using spectrophotometric analysis of the amniotic fluid (optical density [OD] at 450 nm).1 The method to predict the severity of the hemolytic disease of the fetus and neonate was introduced by Liley in 1961.2 The only option in the diagnosis of anemia from causes other than red cell

Fetal MCA: 23 years of literature

Woo and colleagues4 reported serial Doppler flow velocity-time waveforms of the MCA at its origin from the internal carotid arteries in 14 patients with normal singleton pregnancies. The A/B ratio showed a progressive decrease with advancing gestational age. Kirkinen and colleagues5 recorded blood flow velocity waveforms from intracranial arteries in 83 normal and 84 high-risk pregnancies. They concluded that there was a decrease in the resistance index (RI) toward the end of the pregnancy and

MCA-PSV for the diagnosis of fetal anemia: a brief history of its conception

The use of the MCA-PSV for the diagnosis of fetal anemia is considered one of the few practice-changing discoveries in fetal medicine. One of the most important contributions of the MCA-PSV to clinical practice has been the dramatic reduction in the number of invasive procedures performed in the management of red cell alloimmunized pregnancies.25

Mari and colleagues26 reported that the PI of the MCA decreases within 2 hours after intrauterine blood transfusion and that the MCA-PSV was a better

How does the MCA-PSV compare with delta OD450 nm in the diagnosis of anemia?

In 1997, it was reported that the MCA-PSV was at least as good as the delta OD450 in diagnosing anemia; however, it had the advantage of being a noninvasive technique.43 Pereira and colleagues44 confirmed these results. Oepkes and colleagues,39 in a prospective multicenter study, included 165 fetuses of red cell alloimmunized pregnancies with indirect antiglobulin titers of at least 1:64 and antigen-positive fetal blood. The MCA-PSV and delta OD450 methods were applied to all the patients. A

Performing and interpreting the Doppler assessment of the MCA when testing for fetal anemia

The MCA closest to the ultrasound probe should be sampled soon after its origin from the internal carotid artery because the measurement at this level has the lowest intraobserver and interobserver variability, although the peak velocity in the contralateral MCA would still be valid.46, 47 Fig. 3 depicts the area where the spectral Doppler sample volume should be placed once the MCA has been identified. Fig. 4 shows normal and abnormal MCA waveforms.

A total of 50 to 100 waveforms in at least 3

MCA-PSV for the diagnosis of fetal anemia: important considerations in particular scenarios

Important considerations have to be made when using the MCA-PSV for the diagnosis of anemia in fetuses after one or more intrauterine blood transfusions. Detti and colleagues50 examined the MCA-PSV before cordocentesis in 64 fetuses that had previously undergone an intrauterine blood transfusion. Anemia was defined as mild (hemoglobin concentration between 0.65 and 0.84 MoM), moderate (hemoglobin concentration between 0.55 and 0.65 MoM), and severe (hemoglobin concentration <0.55 MoM).

The

Fetal MCA Doppler and IUGR: tracing the concept of IUGR back to its origin

Traditionally, babies born with a low birth weight were likely considered preterm. The concept of IUGR in the literature dates back to the 1960s, when Battaglia and Lubchenco65 and Lubchenco and colleagues66 published their work in which outcomes were recorded based on birth weight adjusted for gestational age. Once such reference values for birth weight by gestational age became available, newborns could be differentiated as small, adequate, or large for gestational age,67 and the concept of

Doppler ultrasonography in the management of IUGR

IUGR represents a threat not only for the fetus but also for the individual as a child and adult. Barker and Osmond73 have described an association between birth weight below the tenth percentile and the later development of hypertension, hypercholesterolemia, coronary heart disease, impaired glucose tolerance, and diabetes mellitus. In utero diagnosis and treatment becomes an appealing approach to reduce the burden exerted by IUGR on society. There are more than 10,000 publications in the

MCA Doppler in the assessment of IUGR fetuses

The structure of the MCA makes it a convenient target for in utero flow velocimetry studies and, at the same time, opens a window to observe the circulation within the central nervous system of the fetus, which is involved in many, if not all, pathologic processes in fetal medicine, including IUGR.

One of the earliest reports on this subject was by Echizenya and colleagues.7 They used pulsed Doppler ultrasonography to examine the significance of MCA flow velocimetry as a fetal assessment tool

MCA PI and RI

The RI and PI were used in most of the initial studies on MCA Doppler in IUGR fetuses, and they continue to represent the mainstay of the assessment in such cases. Ishimatsu and colleagues8 reported lower values of the MCA RI in asymmetrical SGA fetuses when compared with normal and symmetric SGA fetuses. van den Wijngaard and colleagues11 demonstrated a reduced PI in IUGR fetuses when compared with normal fetuses, and these findings were later reproduced.78, 79

Chiba and Murakami80 performed

Reversal of brain sparing effect

An IUGR fetus with a previously low PI that suddenly presents with an elevated MCA PI has been linked to poor outcomes.74 Konje and colleagues85 reported reversal of the brain sparing effect in 8 fetuses, 4 of which ended as stillbirths and the remainder died during the neonatal period.

Rowlands and Vyas86 published a study that included 5 IUGR fetuses that were longitudinally monitored until the time of fetal death. Of the 5 fetuses, 2 developed reversal of the brain sparing effect 48 hours

Reverse end-diastolic flow in the MCA: what does it mean?

Sepulveda and colleagues89 describe a case of IUGR with brain sparing effect, in which the MCA PI increased back to normal limits at 29 weeks of gestation. One week later, reverse end-diastolic flow of the MCA was seen on the day of in utero fetal death. Caution must be exerted when interpreting these data because only 1 case is described, and reverse end-diastolic flow of the MCA can be iatrogenically induced by applying excessive pressure over the fetal cranium.

MCA-PSV: a new parameter in the assessment of IUGR fetuses

Mari and colleagues90 performed a longitudinal assessment of the MCA PI and MCA-PSV in 30 growth-restricted fetuses with an EFW less than the third percentile. Perinatal mortality was recorded, and MCA PI and PSV values were classified as normal or abnormal. Forward stepwise logistic regression indicated that the MCA-PSV was the best parameter in the prediction of perinatal mortality (odds ratio, 14; 95% confidence interval, 1.4–130, P<.05; Nagerlke R[2] = 31). This finding may be explained by

Why is the MCA-PSV increased in IUGR fetuses?

Plausible mechanisms that explain the increase of the MCA-PSV in anemic fetuses have been elucidated, but IUGR fetuses are not necessarily anemic. There must be another reason for the increase in the MCA-PSV in this group of fetuses.

Akalin-Sel and colleagues91 postulated that hypoxemia alone or with hypercapnia is responsible for cerebral vascular responses as part of the complex group of regulatory mechanisms that play a role in the circulatory redistribution in human fetal growth restriction.

Where do the MCA Doppler abnormalities fit in the sequence of abnormal fetal testing in IUGR?

The decreased MCA PI has been historically regarded as an early finding in the sequence of abnormal testing in IUGR, whereas its reversal and an abnormal increase have been described as a late finding.86, 87, 88 Reverse end-diastolic flow in the MCA has been anecdotally described in the literature as an agonal sign, although it is possible to iatrogenically create this when applying pressure over the fetal cranium with the ultrasound probe.89 Hecher and colleagues93 serially assessed 93 IUGR

Performing and interpreting fetal MCA Doppler when IUGR is suspected

The literature on Doppler is saturated with many studies that have performed Doppler analysis on 3 continuous waveforms, selected more often from a group of 5 to 15 waveforms. We believe this is insufficient, especially when basing clinical decisions on these results. This belief has been supported by the results of recent studies.98, 99, 100 Several vessels can have abnormal waveforms following maternal contractions or following a fetal deceleration.101, 102 Therefore, incorrect or unreliable

Summary

The MCA Doppler examination is a great resource in the diagnosis and management of fetal anemia and IUGR. As a window into the hemodynamics of the fetal central nervous system, its potential is clearly unlimited. In cases of IUGR, the MCA Doppler flow velocimetry shows early and late changes. The PSV is proposed as a desirable parameter in every evaluation of IUGR fetuses, particularly because it has been demonstrated to perform better than other parameters in the prediction of perinatal

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