Prenatal ultrasonographic assessment of the middle cerebral artery: a review

Sonographic markers of fetal α-thalassemia major

α-Thalassemia prevails in Southeast Asia, where α-thalassemia major is a lethal type. Sonography is a helpful and cost-effective screening tool for detecting α-thalassemia major fetuses. The cardiothoracic ratio, placental thickness, and middle cerebral artery peak systolic velocity are most used in clinical practice. These sensitive markers are helpful for evaluation of the hemodynamic status and cardiovascular function of the affected fetuses. They can predict fetal α-thalassemia major and assess the efficacy of treatment noninvasively; therefore, the medical costs as well as the possibility of fetal loss caused by invasive procedures can be reduced. Other potentially useful sonographic markers need further studies, although previous preliminary research suggests their usefulness. This article will review those sonographic markers.

Doppler-flow velocity indices in fetal middle cerebral artery in unilateral and bilateral mild ventriculomegaly

OBJECTIVE

To study the association between fetal middle cerebral artery (MCA) Doppler-flow velocity waveforms and the lateral cerebral ventricular width in fetuses diagnosed with unilateral or bilateral ventriculomegaly.

METHODS

A prospective cohort evaluation of the association between Doppler-flow velocity indices of the MCA and ventricular width in singleton fetuses referred because of suspected ventriculomegaly between 20 and 40 weeks' gestation. Fetuses that were diagnosed as bilateral or unilateral ventriculomegaly were assigned to the study group and those with normal ventricular width served as controls.

RESULTS

Of the 53 women recruited to the study, in 30 (57%) fetuses (study group) at least one ventricle ≥ 10 mm was detected, of them 10 (33%) had bilateral ventriculomegaly and 20 (67%) had unilateral ventriculomegaly. Of the 30 fetuses 29 had mild ventriculomegaly. In 23 fetuses ventricular width was <10 mm (control group). Mean MCA pulsatility index (PI) and mean peak systolic velocity (PSV) were not different between the study group and the control group (p=0.935 and p=0.743, respectively). In a linear regression model, MCA-PSV was significantly correlated with gestational age, R(2)=0.309, p<0.001.

DISCUSSION

Unilateral or bilateral mild ventriculomegaly is not associated with fetal MCA change in Doppler-flow velocity indices, suggesting different involvement of vascular component from severe ventriculomegaly.

A primer on antenatal testing for neonatal nurses: part 2: tests of fetal well-being

A number of new antenatal testing tools are being used in obstetric practice to evaluate the clinical picture of the fetus in utero. Results of these tests may prompt transfer to a tertiary facility for delivery or further antenatal monitoring. Part 2 of this 2-part series will describe antenatal testing methods used to determine fetal well-being, as well as highlight the emerging developments in the field of fetal surveillance. The ability to interpret antenatal testing results may help the neonatal team triage to assure bed availability, and predict and provide appropriate staffing for new admissions, and is an important foundation for subsequent neonatal risks and clinical care.

Diagnosis, surveillance, and treatment of the anemic fetus using middle cerebral artery peak systolic velocity measurement

The in utero course of the anemic fetus has improved dramatically, owing to early diagnosis and cordocentesis transfusion. In utero invasive procedures such as amnio- and cordocentesis have become important modalities in the evaluation and treatment of anemic fetuses. However, they carry risks for both the mother and fetus. A valid and sensitive noninvasive means of following the anemic fetus is the evaluation of changes in the middle cerebral artery peak systolic flow velocity (MCA-PSV). This is a sensitive tool for both the evaluation of fetal anemia and response to treatment. Intracerebral vessels respond earliest to the fetal anemic state, and are readily accessible for ultrasound examination. We describe the methodology and evolving clinical applications of MCA-PSV measurement in the fetus, through an overview of the literature describing the development and application of MCA-PSV measurement in fetuses at risk of fetal anemia of various immune and nonimmune etiologies, illustrated by index cases from our center. MCA-PSV measurement is essential in the diagnosis, evaluation, and management of cases of fetal anemia. The use of this modality lessens the need for invasive procedures. The method is readily accessible and should be integrated into the repertoire of all obstetric ultrasound centers.

Ultrasound assessment of the fetal middle cerebral artery peak systolic velocity: a comparison of the near-field versus far-field vessel

OBJECTIVE

Doppler assessment of the fetal middle cerebral artery peak systolic velocity may obviate the need for more invasive procedures in the alloimmunized patient. The purpose of this study was to compare middle cerebral artery peak systolic velocity measurements in the near field and far field.

STUDY DESIGN

Patients between 16 and 42 weeks of gestation with normal fetuses were eligible (n=151). Peak systolic velocity measurements were obtained at the proximal portion of each middle cerebral artery at its origin in the internal carotid artery, as well as the most distal portion before its division, for a total of 4 measurements per fetus. Comparisons were made among the 4 locations and the data were analyzed using a mixed-model analysis of variance adjusted for gestational age. Results were presented using both P values and 95% CIs. P values <.05 were considered statistically significant. Where appropriate, P values and 95% CIs were adjusted using the Tukey multiple comparison procedure. A subanalysis was performed using 11 patients to assess interobserver reliability, which was calculated using the intraclass correlation coefficient (ICC).

RESULTS

All four measurements were obtained for 120 fetuses (79%). The mean gestational age was 27.0 weeks. Statistically significant differences were noted between distal sites (95% CI, -0.05 to 0.01; P<.01) as well as the two sites on each vessel (95% CI, 0.03-0.07 and 0.07-0.12; P<.001 for both vessels). There was no significant difference between the two proximal locations (95% CI, -0.01 to 0.03; P=0.77).

CONCLUSION

By which of the 2 vessels the fetal middle cerebral artery peak systolic velocity is affected is selected, as well as the location on the vessel. If the near-field proximal site cannot be interrogated, the far-field proximal site may be the best alternative.

Doppler sonography of normal fetal vertebral and internal carotid arteries during pregnancy

PURPOSE

The aim of this study was to determine the resistance index (RI) in the fetus in both the vertebral artery and the internal carotid artery and to evaluate the relationship of those RIs with that of the umbilical artery.

METHODS

In this prospective study, color Doppler examinations of the vertebral, internal carotid, and umbilical arteries were performed in fetuses with normal growth between 17 and 41 weeks' gestational age. For every week, the 10th, 50th, and 90th percentiles of the RIs in the 3 arteries plus the ratios of the RIs of the vertebral and umbilical arteries and of the internal carotid and umbilical arteries were calculated.

RESULTS

In 225 examinations in 114 women, the vertebral and internal carotid arteries showed similar RI patterns, with higher RIs at mid gestation. The only difference was that the RIs in the internal carotid artery reached maximum values at a slightly later gestational age (26-28 weeks) than did those in the vertebral artery (24-25 weeks). Also, the RIs in the vertebral artery were slightly higher than were those in the internal carotid artery. RI values in the umbilical artery decreased progressively throughout gestation. Conversely, the ratios of the RIs in the vertebral and umbilical arteries and those of the RIs in the internal carotid and umbilical arteries increased slightly until the end of pregnancy, with the former ratios always higher than the latter ones.

CONCLUSIONS

In normal fetuses, the pattern of blood flow resistance in the vertebral artery resembles that in the internal carotid artery. However, compared with the internal carotid artery, the vertebral artery shows higher absolute RIs with maximum values appearing earlier in the course of pregnancy.

Doppler sonographic study of fetal brachial and umbilical artery blood flow during pregnancy

PURPOSE

The purpose of this study was to evaluate the fetal brachial artery resistance index (RI), its changes throughout gestation, and its relationship to the umbilical artery RI.

METHODS

One hundred fifty-four sonographic examinations of the brachial and umbilical arteries in 71 fetuses were performed between 12 and 40 weeks' gestational age in 71 women with normal pregnancies. For each week of gestational age, the mean, standard deviation, range, and t-distribution 95% confidence interval of the fetal brachial artery RI were calculated.

RESULTS

The fetal brachial artery RI, although relatively lower at the beginning of gestation, showed a pattern of high resistance, with a slight increase until term, whereas the fetal umbilical artery RI decreased progressively.

CONCLUSIONS

The brachial artery RI is high in normal fetuses with good oxygenation. Umbilical artery RIs showed a progressive decrease until the end of term.

Longitudinal survey of blood flow at three different locations in the middle cerebral artery in normal fetuses

OBJECTIVES

To assess vascular impedance at three different locations in the middle cerebral artery (MCA) in normal fetuses throughout gestation.

MATERIALS AND METHODS

Uncomplicated singleton pregnancies at 15-40 weeks' gestation in which Doppler surveys of both MCAs could be obtained were recruited. The pulsatility index (PI) and resistance index (RI) of the proximal, mid and distal sites of both MCAs were measured. The five gestation periods at which the Doppler surveys were performed were (i) 15-19 completed weeks; (ii) 20-24 completed weeks; (iii) 25-29 completed weeks; (iv) 30-34 completed weeks; (v) 35-39 completed weeks.

RESULTS

A total of 42 fetuses were recruited. The average PI/RI values of the proximal, mid and distal MCA were 1.61/0.82, 1.77/0.82, and 1.84/0.84, respectively. The PI value of the proximal MCA was lower than that of the mid and distal MCA. The PI values of the mid and distal MCA showed no difference. The RI value of the MCA from the three locations also showed no difference. The PI/RI values of MCA for each gestational phase were: (i) 1.81/0.87; (ii) 1.79/0.86; (iii) 1.78/0.86; (iv) 1.70/0.81; (v) 1.62/0.77, respectively. Decreased PI/RI values were observed after 30 weeks' gestation.

CONCLUSIONS

The PI values of the proximal MCA are lower than those of the mid and distal MCA. A marked decrease in PI/RI values was observed after 30 weeks' gestation.

Effect of antenatal betamethasone therapy on maternal-fetal Doppler velocimetry

BACKGROUND

The effect of antenatal betamethasone on fetal parameters includes a transient reduction of FHR variation and of fetal body movements. An effect on maternal-fetal blood flow has also been shown, with non-univocal results.

AIMS

To evaluate the effect of antenatal betamethasone in third trimester singleton high-risk pregnancies by Doppler technology.

SUBJECTS AND METHODS

Thirty-six pregnant women who received a full course of betamethasone (12 mg i.m. two times, 24 h apart) were studied. The Doppler examination included the assessment of the pulsatility index (PI) of the umbilical artery (UA PI), the middle cerebral artery (MCA PI) and of resistance index of uterine arteries (Ut RI) before treatment, and 48 and 96 h after second dose of betamethasone.

RESULTS

No significant variation was noted in UA PI through betamethasone therapy. MCA PI decreased significantly 48 h from the last injection of betamethasone (P=0.002), and returned to basal values at 96 h. No difference was found for the other Doppler parameters examined. When serial Doppler studies were analyzed according to the gestational age, in the group <32 weeks' gestation, MCA PI decreased significantly after 48 h (P<0.006) and returned to pre-treatment values after 96 h from the last betamethasone dose. Conversely, no difference was found in Doppler serial measurements in any of the analyzed districts in the subgroup > or =32 weeks.

CONCLUSION

Betamethasone treatment is associated with a significant, although transient, reduction of MCA PI, especially at gestational ages <32 weeks'.

Vascular Doppler techniques

Doppler ultrasound used for the assessment of the fetal umbilical circulation in the human pregnancy has been reported in the scientific literature since the early 1980s and has been rigorously evaluated by randomized, controlled trials. The consensus of the reviewers of these trials is that there do appear to be grounds for including umbilical artery Doppler ultrasound studies in the management of high-risk pregnancies. There is no apparent benefit for low-risk pregnancies or later gestation. Other fetal vascular beds are currently undergoing prospective studies and some limited randomized, controlled trials have been reported; but to date they are not at a point of development to be considered part of clinical management.