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W2000896023 abstract "The use of the middle cerebral artery peak systolic velocity (MCA-PSV) for the diagnosis of fetal anemia has been one of the few discoveries in fetal medicine that is changing the standard of care in the management of affected pregnancies1. This has led to a more than 70% reduction in the number of invasive tests, which often cause fetal death, in the assessment of red-cell alloimmunized pregnancies1. Up to 2 years ago, I thought that only a few doctors in the world were relying upon the MCA-PSV for the diagnosis of fetal anemia. However, in 2003 at the Society for Maternal–Fetal Medicine (SMFM) meeting in San Francisco and a few months later at the American Institute of Ultrasound in Medicine (AIUM) meeting in Montreal, during my lectures on fetal anemia, I asked my colleagues, ‘how many of you are using the middle cerebral artery peak systolic velocity in fetuses at risk of anemia?’, and I was pleasantly surprised to see that about 70% of the participants raised their hands. I then realized that the use of the MCA-PSV in fetal medicine had become a reality. A recent article published in the New England Journal of Medicine entitled ‘Who's on first?—medical discoveries and scientific priority’, illustrates that each achievement in science is usually attributed to the person who made the final contribution to a discovery2. However, behind this person there is the work of many other researchers who prepared the basis for the discovery, and without that work, the discovery would not have been possible. It is for this that I acknowledge the important contribution of many investigators that over the last 20 years have applied Doppler ultrasonography to describe the association between fetal anemia and a hyperdynamic fetal circulation3-11. For me, it all started in 1987 at Baylor College of Medicine, Houston, TX, USA. Along with other investigators, Dr Robert L. Carpenter, Dr Russell L. Deter, Dr Kenneth J. Moise, Jr and Dr Theodor Stefos, I was studying the effects of intravascular transfusion on the circulation of the fetus. We were using two-dimensional (2D) ultrasound equipment (GE PASS II, Milwaukee, WI, USA) that did not have a color Doppler system. I noticed that, in all fetal anemia cases, the MCA waveforms (following transfusion) had a lower PSV value than before transfusion. We reported this concept a number of years later12, 13. I could obtain a clear and good signal from this vessel by placing the sample volume parallel to the greater wing of the sphenoid bone. The anatomy of the MCA suggested that this vessel could be sampled with an angle of zero degrees and, therefore, the blood velocity could be measured. We were able to confirm in every case that the velocity in anemic fetuses was higher than that found following transfusion. Our first study was presented at the Society for Gynecologic Investigation in 199014. In this study, we suggested that, for the diagnosis of fetal anemia, the MCA-PSV was a better parameter than the pulsatility index. In 1995, we reported in this Journal the first comprehensive study on the MCA-PSV15. Our data indicated that we could diagnose fetal anemia in all cases due to red-cell alloimmunization; however, the false-positive rate was approximately 50%. In any case, the measurement of the MCA-PSV could spare 50% of the fetuses at risk for anemia from invasive procedures. I started to apply the MCA-PSV in my practice and I was able to reduce the number of invasive procedures. However, I did not yet understand something related to its application in clinical practice. When I worked at Yale, Dr Uku Oz—a fellow of mine—and I were looking at the correlation between the MCA-PSV and fetal hemoglobin. The data showed that a cubic function described the relationship between the two parameters (Figure 1). Suddenly, I understood what I had missed for a long time: the MCA-PSV does not diagnose all cases of fetal anemia because, in mildly anemic cases, the velocity does not necessarily change. However, the correlation between hemoglobin and MCA-PSV becomes more accurate as the severity of anemia increases16. Furthermore, when the anemia becomes very severe (hemoglobin levels of 1–3 g/dL), the velocity does not increase further. With this information in hand, I organized a study at different medical centers, carried out by several investigators—expert sonologists or good sonographers acquainted with the sampling of the MCA. We measured the velocity prior to cordocentesis in fetuses that were suspected to have anemia, based on traditional criteria. This multicenter study demonstrated that 70% of the invasive procedures performed to diagnose anemia were not necessary because the fetuses were either non-anemic or only slightly anemic1. If we had used the MCA-PSV as the criterion for intervention, we could have avoided approximately 70% of the procedures (Figure 2). In this study, we reported that an exponential function expresses the changes of fetal hemoglobin with advancing gestation, and classified the degrees of anemia as follows: mild, moderate, and severe (Table 1). Because we did not base our decision to perform an invasive procedure on the value of the velocity, I therefore participated in another study with Dr Roland Zimmerman, chairman of Obstetrics and Gynecology at the University of Zurich, Switzerland, Dr Robert L. Carpenter from the Houston Medical Center, and Dr Peter Duerig from Bern University, Switzerland. Dr Zimmerman and I had discussed this project in 1996 but we had not pursued it. Now the time was right. In this study, we based our decision to perform an invasive procedure on an elevated MCA-PSV value17. We included 125 women at risk for having a fetus with anemia, and avoided any invasive procedure in 90 women. We detected all but two cases of moderate and severe anemia. The first was a case in which the last value of velocity was assessed 3.5 weeks prior to delivery. The fetus was delivered at 35.5 weeks and the hematocrit was 24.5%. The second case was that of a patient serially followed up to 35 weeks when the last measurement was obtained. The fetus was then delivered 2.5 weeks later and the hematocrit was 15%. The neonates were transfused and did well. We also induced labor in six patients after 35 weeks' gestation because the value of the velocity was above our cut-off point. The neonates were not anemic. This study taught us that in some fetuses the MCA-PSV should be evaluated more frequently than every 2–3 weeks, and following 35 weeks' gestation, the MCA-PSV false-positive rate increases. I believe that the reason why the MCA-PSV, following 35 weeks' gestation, may be falsely increased in normal, non-anemic fetuses is due to different behavioral states of the fetus in this period of gestation. For example, the MCA-PSV may be falsely increased when the measurement is performed during a period of rest that follows a period of fetal activity. For the management of the fetus at risk for anemia following 35 weeks, see Figures 3 and 4. Cubic function describing the relationship between middle cerebral artery peak systolic velocity (MCA-PSV) and fetal hemoglobin (Hb). The values are expressed as multiples of the median (MoM). y = 0.6835 + MCA-PSV MoM × 1.2794 − 1.2885 MCA-PSV2 + 0.2861 × MCA-PSV3. Peak velocity of systolic blood flow in the middle cerebral artery (MCA) with advancing gestation. The curves indicate the median (below) and 1.5 multiples of the median (MoM) (above) peak systolic velocity (PSV) in the MCA. (Reprinted from G. Mari et al. N Engl J Med 2000; 342: 9–141, with permission. Copyright © 2000 Massachusetts Medical Society). Algorithm for the management of red-cell alloimmunization (Part I). Although it is commonly reported that fetal anemia develops with an antibody titer of at least 1 : 16, with some antigens, i.e. Kell, severe fetal anemia may develop with a lower value (personal experience). MCA-PSV, middle cerebral artery peak systolic velocity; PCR, polymerase chain reaction; RhD, rhesus D. Algorithm for the management of red-cell alloimmunization (Part II). GA, gestational age; MoM, multiples of the median; MCA-PSV, middle cerebral artery peak systolic velocity. In a subsequent study, Detti et al. reported that the MCA-PSV could be used to diagnose anemia even in fetuses previously transfused once18. The Rh blood group system was discovered by Landsteiner and Weiner in 194019 and its involvement in maternal alloimmunization and hemolytic disease of the fetus and neonate (HDFN) was first described by Levine et al. in 194120. In 1953, Bevis first recognized that spectrophotometric measurements of amniotic fluid appeared to change at optical density 450 nm in fetuses who were shown to have HDFN21. In 1956, Liley performed the first amniocentesis in a human to assess the fetal bilirubin through a spectrophotometric analysis in a pregnancy at risk for anemia, and in 1960 he described the technique and complications of amniocentesis22. In 1961, Liley described a method which uses the observed change in the optical density at 450 nm (delta OD450) to predict the severity of HDFN in fetuses23, and in 1963 this investigator performed the first intrauterine transfusion (intraperitoneal) in an anemic fetus using X-ray guidance24. In 1964, Freda et al. performed the first intravascular transfusion in a fetus at 26 weeks' gestation25. This was the first case of open fetal surgery. Early in the 1970s, Carlo Valenti performed the first fetoscopy and also the first umbilical blood sampling under fetoscopy guidance26, 27. This technique was extensively used in Europe by Dr Charles Rodeck and his group28, and in the United States by Dr John Hobbins and Dr Jeremiah Mahoney29. In 1983, fetal blood sampling under ultrasound guidance was described by Daffos et al.30 and it remains the current technique used for fetal blood transfusion. Despite the introduction of Rh(D) immune globulin for the prevention of hemolytic disease of the fetus/newborn following the studies of Vincent Freda and collaborators31-33, who received the Lasker award in 1980, Rh alloimmunization remains a major problem in several areas of the world. Maternal Rh alloimmunization occurs when a pregnant woman develops an immunological response to a paternally derived red blood cell antigen (D) foreign to the mother and inherited by the fetus. The antibodies may cross the placenta, bind to antigens present on the fetal erythrocytes, and cause hemolysis. Hemolysis of the erythrocytes causes anemia in the fetus, and if severe, may result in edema, hydrops fetalis, and fetal death. Hemolytic disease of the fetus/neonate can also be caused by other antigens of the Rh blood group system and by the so-called ‘irregular antigens’ of the non-rhesus blood group system. Therefore, the term red-cell alloimmunization is more commonly used. Red-cell alloimmunization remains the most common cause of fetal anemia even in the USA, as a recent review of the 2001 birth certificates by the Centers for Disease Control and Prevention indicates that Rh sensitization still affects 6.7 out of every 1,000 live births34. This number, added to the other causes of red-cell alloimmunization (Kell, Kidd, Duffy, etc.), suggests that each year in the USA there are more than 30 000 fetuses at risk for anemia due to red-cell alloimmununization. In 1997, we reported that the MCA-PSV is superior to amniocentesis in detecting anemia in cases at risk of anemia35. Pereira et al. in 2003, confirmed these results36. A recent, comprehensive, multicenter study by Oepkes et al., in which MCA-PSV and amniocentesis were performed prior to cordocentesis, has reported that the sensitivity and specificity of the MCA-PSV for detection of anemia are better than amniocentesis, which was considered the standard of care to diagnose fetal anemia in red-cell alloimmunization cases, and MCA can be safely used for timing a cordocentesis and possible fetal transfusion37. In their study, the authors used both the Liley23 and the Queenan38 curves. Bullock et al. have reported, in this issue of the Journal, that MCA-PSV and delta OD450 have similar test accuracy in detecting fetal anemia39. However, they conclude that the MCA-PSV is a preferable screening method for fetal anemia because it is non-invasive. The MCA-PSV diagnoses fetal anemia, even in cases of Kell sensitization, in which the problem is not the hemolysis but the suppression of the erythroid precursor in the bone marrow. We found a good correlation between the blood velocity and the hemoglobin values (R2 = 55%)1. Van Dongen et al., in this issue of the Journal, concisely confirm that MCA-PSV can be used even in cases of Kell alloimmunization40. This is another advantage of using the MCA-PSV, because in cases of Kell alloimmunization, delta OD450 is not accurate41-43. I do not see any problem with investigators expressing the concept of anemia in SD or in absolute values, or when they develop reference ranges for the MCA-PSV in the normal fetuses in their population. However, I do see a problem when investigators—not trained to correctly sample this parameter—perform a study on fetuses at risk for anemia, and try to predict this condition by using the MCA-PSV. This can be misleading, which is highlighted in the article by Bartha et al., reported in this issue of the Journal44. The sensitivity of the MCA-PSV for the diagnosis of fetal anemia ranged from 7% to 100% in the hands of different operators1, 40, 44-50. Therefore, the operators should be trained to correctly sample the MCA-PSV, for if the measurement is done well, the intra- and interobserver variabilities are small. Another important issue is determining what part of the MCA should be sampled. I completed a study on the intra- and interobserver variabilities of the MCA with Dr Alfred Abuhamad, Dr Mekibib Altaye, and three of my former fellows: Dr Erich Cosmi, Dr Maria Segata, and Dr Masashi Akiyama51. The results indicate that any segment of the MCA, with the exception of the area close to its division into terminal branches, can be sampled with good results. The reason why the distal area of the MCA does not have good reproducibility is due to a technical factor: any minimal movement of the fetal head can displace the sample volume in one of the terminal branches. There are usually two or three terminal branches but in my experience there can be as many as five (Figure 5). The MCA-PSV should be sampled at its proximal point, soon after its origin from the internal carotid artery, avoiding the need for angle correction, because measurement at this point is associated with the lowest intra- and interobserver variabilities51. The sample volume should be placed at the center of the vessel (Figure 6). If this Doppler parameter is correctly measured, the differences in the MCA-PSV reference ranges that different investigators might find would be minimal. Although the possibility exists that I may miss a case of severe anemia in the future, I feel very fortunate because, to date, while managing patients at risk for fetal anemia using the MCA-PSV reference ranges previously reported, I have never missed a case of moderate or severe anemia. Therefore, I do not believe that the cut-off points we have previously generated should be modified, since the curve was obtained with data gathered by several experienced investigators at different centers. Color Doppler ultrasound image showing the middle cerebral artery (MCA). (a) The main trunk divides into two terminal branches (indicated by arrows 1 and 2); (b) it divides into five terminal branches (1 to 5); (c) double MCA (normal variant); (d) color Doppler of the MCA (top); flow velocity waveforms of the MCA (above the baseline) and lenticulostriates arteries (ART-LS) (below the baseline). Color Doppler ultrasound image showing the middle cerebral artery. The sample volume (arrow) is placed in the center of the vessel after its origin from the internal carotid artery. When the MCA is sampled, it is important to be aware and recognize the possible variants of this vessel (double MCA), or the waveforms of its collaterals (lenticulostriates arteries) (Figure 5). I believe that the blood velocity is increased in any vessel of the severely anemic fetus, as also suggested by the study by Van Dongen et al. reported in this issue of the Journal40. The advantage of studying the MCA is that it is easy to get an angle of zero degrees between the ultrasound beam and the direction of blood flow. In the diagnosis of severe anemia, there is one finding—tricuspid regurgitation—that precedes the development of ascites and hydrops. Use of this parameter could be of help in decreasing the false-negative cases. If a fetus at risk for anemia has a normal MCA-PSV and tricuspid regurgitation is present, it would be important to follow that fetus very closely, because it could be anemic. Although tricuspid regurgitation can be found in normal and non-anemic fetuses, in my experience, it is very unlikely to be found in fetuses at risk for anemia, especially when there is holosystolic regurgitation. I believe that if a sonologist is well trained in the measurement of the MCA-PSV, the management of a patient at risk for fetal anemia can be based on the MCA-PSV; if the sonologist is not trained properly, it is better to use a different strategy to diagnose fetal anemia. For example, the patient could be referred to the closest center that has sonologists or sonographers trained to correctly measure the MCA-PSV. If there are no close centers that perform the MCA-PSV assessment, the patient should be informed of this limitation. The option of assessing fetal anemia with an invasive and less sensitive procedure than MCA-PSV assessment, such as amniocentesis, should be presented to the patient. It is important to emphasize that MCA-PSV assessment should be reserved for those patients who are at risk of having an anemic fetus—indiscriminate use of the MCA-PSV without a clear indication may cause more harm than good. It is neither wise nor good medical care to screen every patient with the MCA-PSV and if the value is elevated, to assume that the fetus is anemic. This may create unnecessary anxiety and iatrogenic investigation. For example, if fetal–maternal hemorrhage is suspected, because of absent fetal movements and sinusoidal fetal heart rate tracing, an elevated MCA-PSV may strengthen the suspicion. On the other hand, an elevated MCA-PSV, in the presence of a reassuring fetal heart rate tracing and no anemia risk, does not indicate pathology—it may represent a false-positive case. Therefore, no intervention is indicated when an elevated MCA-PSV value is found in the absence of the risk of fetal anemia. Since our first studies on the cerebral circulation of the anemic fetus, we have sampled the MCA following its origin from the internal carotid artery1, 15. Recently, we have emphasized the steps for the correct measurement of the MCA-PSV: a) an axial section of the head is obtained at the level of the sphenoid bones; b) color Doppler identifies the circle of Willis; c) the image of the circle of Willis is enlarged; d) the color box is placed around the MCA; e) the MCA is zoomed; f) the MCA flow velocity waveforms are displayed and the highest point of the waveform (PSV) is measured. The waveforms should be all similar. The above sequence is repeated at least three times in each fetus51. I have trained many sonographers and sonologists on the use of the MCA-PSV. In the USA, it is not plausible to request board-certified physicians to demonstrate their skill in the measurement of the MCA-PSV. However, I feel that each sonographer and sonologist interested in the measurement of the MCA-PSV should have the possibility of contacting one center for advice. I believe that the first step for achieving good training should be a course on the application of MCA-PSV for the diagnosis of fetal anemia; this should be followed by practical application, i.e. availability to compare the measurement with that obtained by a trained sonographer or sonologist. Our center, in Detroit, Michigan, USA, is available for review of both images and tapes to sonographers and sonologists interested in improving their skill. Today, I manage patients at risk for anemia because of red-cell alloimmunization, as indicated in Figures 3 and 4. Two known methods are used in assessing the sequential studies of the MCA-PSV given in these flow charts. The first method requires a mathematical approach. When, for the first time, I meet a patient who is at risk of having an anemic fetus due to red-cell alloimmunization, I measure the MCA-PSV. If the value is below 1.5 multiples of the median (MoM) (Figure 2), I reassess the MCA-PSV in 1 week. If the value remains below 1.5 MoM, I reassess the parameter the following week. Afterwards, I perform a linear regression analysis on the three values, and if the line is to the right of the thin curve shown in Figure 7, I repeat the study at intervals that vary between 2 and 4 weeks, based on the risk of the patient52. For example, if I see a patient for the first time at 16 weeks and (a) she has an anti-c value of 1 : 16, (b) the father of her baby is heterozygous for the c factor, (c) she is not interested in having an amniocentesis to know if the fetus is c positive, and (d) she does not have a history of a previous baby affected by anemia, I reassess the MCA-PSV in 4 weeks. Afterwards, I base my decision for a repeat test on the trend of the MCA-PSV. If the line remains to the right of the thin curve shown in Figure 7, and the value remains below 1 : 128, I repeat the scan every 2 weeks until 35 weeks. At this gestational age, if the value remains below the cut-off of 1.5 MoM, I continue to follow the MCA-PSV on a weekly basis. If the value is above 1.5 MoM, I evaluate the trend of the MCA-PSV and if it increases, following the administration of steroids to the mother, I induce labor, as indicated in Figure 4. Average regression line for non-anemic fetuses (dashed line, y = −17.28 + 1.99x); mildly anemic fetuses (thin line, y = −53.54 + 4.17x) and severely anemic fetuses (thick line, y = −76.82 + 5.26x). (Reprinted from Detti L. et al.52, © 2002, with permission from Elsevier). Of note is that, if the patient is Rh negative, I perform a maternal blood test to check for RhD genotype of the fetus. This new technique is very accurate and avoids the risk of the amniocentesis53-55. An alternative to the above management is to assess the MCA-PSV on a weekly basis. If it becomes higher than 1.5 MoM, one should repeat the study in 2–3 days, and if the value continues to increase, one should perform a cordocentesis and be ready for intravascular transfusion. The MCA–PSV median and 1.5 MoM are reported in Table 2. MCA-PSV can be used to diagnose fetal anemia due to other causes. Delle Chiaie et al.46 and Cosmi et al.45 reported that this parameter is useful in cases of fetal anemia secondary to parvovirus infection. Senat et al.56 reported that MCA-PSV diagnoses anemia secondary to twin–twin transfusion syndrome (TTTS), and others have reported that MCA-PSV diagnoses anemia secondary to fetomaternal hemorrhage57, 58, and fetal hydrops59, 60. In cases with parvovirus infection, I perform an ultrasound every week for 10 weeks following the exposure. I look for signs of anemia and I evaluate the MCA-PSV. If the value of the velocity becomes higher than 1.5 MoM, I repeat the ultrasound examination twice a week, and look for tricuspid regurgitation and ascites. Often, I do not intervene in cases of parvovirus infection based solely on the MCA-PSV because the fetus would not necessarily become hydropic, and the anemia might resolve spontaneously without intervention. Fetal–maternal hemorrhage usually occurs in the third trimester. When I diagnose fetal–maternal hemorrhage, I perform a Cesarean delivery. The MCA-PSV is elevated in cases of fetal–maternal hemorrhage, but as indicated above, I utilize other signs that might suggest fetal–maternal hemorrhage (absence of fetal movements, sinusoidal pattern in the fetal heart rate tracing) prior to assessing the MCA-PSV. In non-immune hydrops, if the MCA-PSV is below the cut-off point of 1.5 MoM, I do not perform a cordocentesis. The preliminary data of Senat et al. appear promising for the use of MCA-PSV in the management of monochorionic twins following the death of the co-twin56. Recently, Robyr et al. have reported that in TTTS, feto-fetal hemorrhage from recipient to donor occurs in 10% of cases with double survivors as a result of incomplete laser coagulation of anastomoses61. Therefore, this parameter should be used for follow-up cases of TTTS following laser therapy. In conclusion, the MCA-PSV has been shown to be an excellent tool for the diagnosis of fetal anemia. The condicio sine qua non for correctly measuring this parameter is the training of sonographers and sonologists. I believe that centers managing anemic fetuses should become comfortable with the diagnosis of fetal anemia using the MCA-PSV. I would like to thank Dr Russell L. Deter and Dr Roberto Romero for their lifelong support and friendship." @default.
W2000896023 created "2016-06-24" @default.
W2000896023 creator A5055472404 @default.
W2000896023 date "2005-03-24" @default.
W2000896023 modified "2023-09-27" @default.
W2000896023 title "Middle cerebral artery peak systolic velocity for the diagnosis of fetal anemia: the untold story" @default.
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W2000896023 doi "https://doi.org/10.1002/uog.1882" @default.
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