Fetal cardiac output in the isoimmunized pregnancy: a pulsed Doppler-echocardiographic study of patients undergoing intravascular intrauterine transfusion

Automated quantitative evaluation of fetal atrioventricular annular plane systolic excursion before and after intrauterine blood transfusion in pregnancies affected by red blood cell alloimmunization

INTRODUCTION

Maternal red blood cell alloimmunization during pregnancy can lead to hemolysis and various degrees of fetal anemia, which can be treated with intrauterine blood transfusion (IUT) to prevent adverse outcomes. Knowledge about fetal myocardial function and adaptation is limited. The aim of the present study was to measure fetal atrioventricular plane displacement before and after IUT and compare these measurements with previously established reference ranges.

MATERIAL AND METHODS

An observational study was conducted on pregnant women affected by red blood cell alloimmunization. Fetal echocardiography was performed before and after IUT. The atrioventricular plane displacement of the left and right ventricular walls and interventricular septum, described as mitral, septal, and tricuspid annular plane systolic excursion (MAPSE, SAPSE, and TAPSE, respectively), was assessed using color tissue Doppler imaging with automated analysis software. A Mann-Whitney U test was used to compare the z scores to the normal mean before and after IUT.

RESULTS

Twenty-seven fetuses were included. The mean z score for pre-IUT MAPSE was significantly increased compared with the reference ranges, +0.46 (95% confidence interval [CI] +0.17 to +0.75; p = 0.039), while the mean z scores for post-IUT SAPSE and TAPSE were significantly decreased, -0.65 (95% CI -1.11 to -0.19; p < 0.001) and -0.60 (95% CI -1.04 to -0.17; p = 0.003), respectively. The difference in atrioventricular plane displacement z scores before and after IUT was statistically significant in all three locations. The median difference between the pre-IUT and post-IUT z scores was -0.66 (95% CI -1.03 to -0.33, p < 0.001) for MAPSE, -1.05 (95% CI -1.43 to -0.61, p < 0.001) for SAPSE, and -0.60 (95% CI -1.19 to -0.01, p = 0.046) for TAPSE.

CONCLUSIONS

This study suggests that atrioventricular plane displacement, when determined using automated analysis software, may represent a quantitative parameter, describing fetal myocardial function and adaptation before and after IUT.

Minute Stroke Distance Is a More Reproducible Measurement Than Cardiac Output in the Assessment of Fetal Ventricular Systolic Function

BACKGROUND

Echocardiographic quantification of fetal cardiac output (CO) aids clinical decision-making in the management of various cardiac and extracardiac diseases. Small variability in measuring semilunar valve dimension significantly reduces the reproducibility of the calculated CO. The authors propose minute stroke distance or velocity-time integral (VTI) as a more reproducible measure reflecting fetal ventricular systolic function. The aim of this study was to test the hypothesis that right and left ventricular minute VTI increase predictably with estimated fetal weight and are more reproducible than CO.

METHODS

Five hundred seventy-one singleton fetuses without cardiovascular pathology between 16 and 36 weeks' gestation were reviewed retrospectively. Twenty-two fetuses with pathology resulting in low- or high-CO states were also assessed for comparison. VTI was measured in both ventricular outflow tracts at the level of the semilunar valve, excluding a Doppler insonation angle of >30°. Heart rate, semilunar valve dimension, and VTI determined minute VTI and CO. Inter- and intrarater variability were evaluated in a random 10% subset.

RESULTS

Minute VTI and CO measurements were feasible in 67% to 89% of fetuses in this retrospective study. Minute VTI and CO increased with estimated fetal weight nonlinearly (R = 0.61-0.94). The mean inter- and intrarater variability for VTI, 6% and 5.7%, were significantly less than for CO, 25% and 23.7% (P < .001 for all).

CONCLUSIONS

Minute VTI is an easily measured, highly reproducible method of quantifying fetal ventricular systolic function. Variability in calculated CO from valve measurement differences is minimized by solely using VTI. Nomograms of minute VTI provide an efficient and precise assessment of fetal systolic function and may be used to track fetuses in disease states with low or high CO.

Decreased fetal cardiac output in pregnant women with severe SARS-Cov-2 infection

AIM

We aimed to examine fetal cardiac output (CO) in patients who recovered from severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) infection.

MATERIALS

This prospective study included 48 pregnant women recovered from SARS-CoV-2 infection and 50 control cases. SARS-CoV-2 infection was diagnosed by polymerase chain reaction (PCR) test in patients. Fetal echocardiographic evaluations were performed at 24-37 weeks of gestation in pregnant women who recovered from the infection and control group.

RESULTS

The median value of ultrasound evaluation was 34 (2.6) weeks of gestation in the recovery from the SARS-CoV-2 infection (RSI) group, and 32 (7.6) weeks in the control group (p = .565). Left cardiac output (LCO) z score was significantly lower in the RSI group than the control group (p = .041). LCO and combine cardiac output (CCO) z score were significantly lower in the severe disease group than mild, moderate disease groups, and controls (p = .019 and p = .013). CCO (ml/min/kg) was decreased in the severe disease group when compared with control and mild disease groups (p = .044).

CONCLUSION

In the present study, fetal cardiac output in pregnant women who recovered from SARS-CoV-2 infection was found to be significantly reduced in those with severe disease, while there was no significant difference in mild and moderate cases. Placental dysfunction and inflammatory cytokines might cause fetal cardiac changes. Further studies could be clarified on the impact of SARS-CoV-2 infection on fetal cardiac function.

Fetal cardiac function at intrauterine transfusion assessed by automated analysis of color tissue Doppler recordings

BACKGROUND

Fetal anemia is associated with a hyperdynamic circulation and cardiac remodeling. Rapid intrauterine transfusion (IUT) of blood with high hematocrit and viscosity into the umbilical vein used to treat this condition can temporarily further affect fetal heart function. The aim of this study was to evaluate the short-term changes in fetal myocardial function caused by IUT using automated analysis of cine-loops of the fetal heart obtained by color tissue Doppler imaging (cTDI).

METHODS

Fetal echocardiography was performed before and after IUT. cTDI recordings were obtained in a four-chamber view and regions of interest were placed at the atrioventricular plane in the left ventricular (LV), right ventricular (RV) and septal walls. Myocardial velocities were analyzed by an automated analysis software to obtain peak myocardial velocities during atrial contraction (Am), ventricular ejection (Sm), rapid ventricular filling (Em) and Em/Am ratio was calculated. Myocardial velocities were converted to z-scores using published reference ranges. Delta z-scores (after minus before IUT) were calculated. Correlations were assessed between variables and hemoglobin before IUT.

RESULTS

Thirty-two fetuses underwent 70 IUTs. Fourteen were first time transfusions. In the LV and septal walls, all myocardial velocities were significantly increased compared to normal values, whereas in the RV only Sm was increased before IUT (z-scores 0.26-0.52). In first time IUTs, there was a negative correlation between LV Em (rho = - 0.61, p = 0.036) and LV Em/Am (rho = - 0.82, p = 0.001) z-scores and hemoglobin before IUT. The peak myocardial velocities that were increased before IUT decreased, whereas LV Em/Am increased significantly after IUT.

CONCLUSIONS

This study showed that peak myocardial velocities assessed by cTDI are increased in fetuses before IUT reflecting the physiology of hyperdynamic circulation. In these fetuses, the fetal heart is able to adapt and efficiently handle the volume load caused by IUT by altering its myocardial function.

Fetal Programming of Cardiac Function and Disease

Fetal programming describes long-term adaptive changes that an organism undergoes in response to an intrauterine insult. This term was coined to describe the increased incidence of adult disease, such as cardiovascular disease, seen among populations that suffered an intrauterine insult. While changes induced by such an insult may be initially beneficial, they can have deleterious long-term effects. Cardiac programming effects can be induced by maternal diet alterations, fetal exposure to increased levels of corticosteroids, chronic fetal hypoxia and anemia, and maternal use of nicotine or cocaine. These stimuli result in a variety of changes in cardiac function and gene expression, many of which persist into adulthood. A possible mediator of these changes is an alteration in the DNA methylation pattern of the cardiomyocytes. This review gives an overview of the changes that have been observed in the heart in response to various programming stimuli and potential programming mechanisms.

Diagnosis and treatment of fetal cardiac disease: a scientific statement from the American Heart Association

BACKGROUND

The goal of this statement is to review available literature and to put forth a scientific statement on the current practice of fetal cardiac medicine, including the diagnosis and management of fetal cardiovascular disease.

METHODS AND RESULTS

A writing group appointed by the American Heart Association reviewed the available literature pertaining to topics relevant to fetal cardiac medicine, including the diagnosis of congenital heart disease and arrhythmias, assessment of cardiac function and the cardiovascular system, and available treatment options. The American College of Cardiology/American Heart Association classification of recommendations and level of evidence for practice guidelines were applied to the current practice of fetal cardiac medicine. Recommendations relating to the specifics of fetal diagnosis, including the timing of referral for study, indications for referral, and experience suggested for performance and interpretation of studies, are presented. The components of a fetal echocardiogram are described in detail, including descriptions of the assessment of cardiac anatomy, cardiac function, and rhythm. Complementary modalities for fetal cardiac assessment are reviewed, including the use of advanced ultrasound techniques, fetal magnetic resonance imaging, and fetal magnetocardiography and electrocardiography for rhythm assessment. Models for parental counseling and a discussion of parental stress and depression assessments are reviewed. Available fetal therapies, including medical management for arrhythmias or heart failure and closed or open intervention for diseases affecting the cardiovascular system such as twin-twin transfusion syndrome, lung masses, and vascular tumors, are highlighted. Catheter-based intervention strategies to prevent the progression of disease in utero are also discussed. Recommendations for delivery planning strategies for fetuses with congenital heart disease including models based on classification of disease severity and delivery room treatment will be highlighted. Outcome assessment is reviewed to show the benefit of prenatal diagnosis and management as they affect outcome for babies with congenital heart disease.

CONCLUSIONS

Fetal cardiac medicine has evolved considerably over the past 2 decades, predominantly in response to advances in imaging technology and innovations in therapies. The diagnosis of cardiac disease in the fetus is mostly made with ultrasound; however, new technologies, including 3- and 4-dimensional echocardiography, magnetic resonance imaging, and fetal electrocardiography and magnetocardiography, are available. Medical and interventional treatments for select diseases and strategies for delivery room care enable stabilization of high-risk fetuses and contribute to improved outcomes. This statement highlights what is currently known and recommended on the basis of evidence and experience in the rapidly advancing and highly specialized field of fetal cardiac care.

A case of alloimmune thrombocytopenia, hemorrhagic anemia-induced fetal hydrops, maternal mirror syndrome, and human chorionic gonadotropin-induced thyrotoxicosis

Fetal/neonatal alloimmune thrombocytopenia (FNAIT) can be a cause of severe fetal thrombocytopenia, with the common presentation being intracranial hemorrhage in the fetus, usually in the third trimester. A very unusual case of fetal anemia progressed to hydrops. This was further complicated by maternal Mirror syndrome and human chorionic gonadotropin-induced thyrotoxicosis. Without knowledge of etiology, and possibly due to associated cardiac dysfunction, fetal transfusion resulted in fetal demise. Subsequent testing revealed FNAIT as the cause of severe hemorrhagic anemia. In cases with fetal anemia without presence of red blood cell antibodies, FNAIT must be ruled out as a cause prior to performing fetal transfusion. Fetal heart may adapt differently to acute hemorrhagic anemia compared with a more subacute hemolytic anemia.

Myocardial performance and its acute response to angiotensin II infusion in fetal sheep adapted to chronic anemia

Fetal chronic anemia causes lengthening of cardiomyocytes. In adults, severe left ventricular overload may lead to irreversible ventricular dysfunction. We hypothesized that in sheep fetuses with chronic anemia, remodeled myocardium would less successfully respond to angiotensin II (AT II) infusion than in fetuses without anemia. A total of 14 ewes with twin pregnancy underwent surgery at 113 ± 1 days of gestation. After a recovery period, anemia was induced by isovolumic hemorrhage in 1 fetus of each pair. At 126 ± 1 days of gestation, longitudinal myocardial velocities of the right (RV) and left (LV) ventricles were assessed at the level of the atrioventricular valve annuli via tissue Doppler imaging. Cardiac outputs were calculated by pulsed Doppler ultrasound. All measurements were performed at baseline and during fetal AT II infusion. Fetal serum cardiac natriuretic peptide (N-terminal peptide of proatrial natriuretic peptide [NT-proANP] and B-type natriuretic peptide [BNP]) concentrations were determined. Nine ewes successfully completed the experiment. At baseline, ventricular free wall thicknesses, cardiac outputs, and NT-proANP levels were significantly greater in the anemic fetuses than in the controls. The LV isovolumic contraction velocity (IVCV) acceleration and isovolumic relaxation velocity (IVRV) deceleration were lower (P < .05) in the anemic fetuses than in the controls. In the anemic fetuses, there was a positive correlation (R = .93, P < .01) between RV IVRV deceleration and NT-proANP concentration. Angiotensin II infusion increased (P < .05) LV IVCV acceleration in the anemic fetuses. We conclude that in anemic sheep fetuses, myocardial adaptation is associated with impaired LV early contraction and relaxation. However, the LV can improve its contractility with an inotropic stimulus, even in the presence of increased afterload.

Fetal cardiac output in monochorionic twins

OBJECTIVES

To compare fetal cardiac output (CO) in donor and recipient twins of twin-twin transfusion syndrome (TTTS) pregnancies after laser therapy with that of monochorionic twins without TTTS and normal singletons.

METHODS

In a longitudinal, prospective study, we sonographically assessed fetal CO in donors (n = 10) and recipients (n = 10) with TTTS after fetoscopic laser therapy, in monochorionic twins without TTTS (n = 20) and in normal singleton pregnancies (n = 20). The fetal CO of TTTS twins was determined 1 day and 1 week after laser treatment, and from then on every 2-4 weeks until birth. Twins without TTTS were examined biweekly until birth. Singletons were examined twice, with an 8-week interval, at different gestational ages between 17 and 35 weeks.

RESULTS

Absolute CO increased exponentially with advancing gestational age (P < 0.0001), and was significantly related to fetal weight in all groups (P < 0.0001). The median CO/kg in donors after laser therapy, recipients after laser therapy and non-TTTS monochorionic twins was significantly higher than that in singletons (all P < 0.001). Median CO/kg in donors after laser therapy, recipients after laser therapy, and non-TTTS monochorionic twins was not significantly different between groups.

CONCLUSIONS

Monochorionic twins with TTTS have higher CO after laser therapy than normal singletons.

Assessing fetal cardiac ventricular function

Fetal echocardiography has been used primarily to identify fetuses with structural malformations of the heart. Evaluation of fetal ventricular function, however, has received minimal attention since the inception of fetal echocardiography in the early 1980s. This communication reviews the use of M-mode, B-mode and pulsed Doppler ultrasound to examine cardiac function. M-mode ultrasound is used to determine the size of the fetal heart, the end-diastolic and end-systolic dimensions of the ventricular chambers, and the thickness of the ventricular walls and the interventricular septum, and to measure the diameter of the mitral and tricuspid valves as well as the diameter of the aorta and pulmonary artery. B-mode evaluation of the fetal heart includes measurement of atrial and ventricular dimensions as well as dimensions of the outflow tracts. This modality is useful when M-mode measurements cannot be made due to fetal position. Once measurements of cardiac structures are obtained using either M-mode or B-mode ultrasound, pulsed Doppler recording of mitral valve, tricuspid valve, aortic valve and pulmonary artery waveforms can be used to compute cardiac output as well as stroke volume. In addition, pulsed Doppler can be used to evaluate diastolic and systolic cardiac functions by examining the components of each waveform.

Fetal cardiac contractility before and after intrauterine transfusion

OBJECTIVE

To evaluate the effect of fetal anemia and intrauterine transfusion on ventricular shortening fraction.

METHODS

The end-diastolic and end-systolic transverse dimensions of the left and right ventricles were obtained using M-mode ultrasonography. The shortening fractions of both ventricles were calculated at three time points: before, immediately after and one day after intrauterine transfusion. The blood volume given at intrauterine transfusion was expressed as a percentage of estimated fetoplacental blood volume.

RESULTS

Complete measurements were obtained from 49 transfusions in 23 fetuses. Intrauterine transfusion was performed at a median gestational age of 31 (range, 19-35) weeks. Median hemoglobin concentration before and after intrauterine transfusion was 7.9 (range, 2.7-13.7) g/dL and 14.3 (range, 12.7-16.1) g/dL, respectively. Both left and right ventricular shortening fractions differed significantly between the three time points. Left ventricular shortening fraction decreased immediately after transfusion in 43 (88%) of the 49 procedures. Right ventricular shortening fraction decreased immediately after transfusion in 42 (86%) of the 49 procedures. At the first intrauterine transfusion, there was only a weak correlation between the decrease in shortening fraction of both ventricles and the transfused volume (left: R(2) = 0.15; P = 0.20/right: R(2) = 0.005; P = 0.81).

CONCLUSION

Transfusion significantly decreases the shortening fraction of both ventricles of the fetal heart. There is, however, little correlation between the decrease in shortening fraction and the volume of red cells given at intrauterine transfusion. Published by John Wiley & Sons, Ltd.

Red Blood Cell Alloimmunization in Pregnancy

Red blood cell (RBC) alloimmunization in pregnancy continues to occur despite the widespread use of both antenatal and postpartum Rhesus immune globulin (RhIG), due mainly to inadvertent omissions in administration as well as antenatal sensitization prior to RhIG given at 28 weeks' gestation. Additional instances are attributable to the lack of immune globulins to other RBC antigens. Evaluation of the alloimmunized pregnancy begins with the maternal titer. Once a critical value [32 for anti-Rh(D) and other irregular antibodies; 8 for anti-K and -k] is reached, fetal surveillance using serial Doppler ultrasound measurements of the peak velocity in the fetal middle cerebral artery (MCA) is standard. In the case of a heterozygous paternal phenotype, amniocentesis can be performed to detect the antigen-negative fetus that requires no further evaluation. MCA velocities greater than 1.5 multiples of the median necessitate cordocentesis, and if fetal anemia is detected, intrauterine transfusion therapy is initiated. A perinatal survival of greater than 85% with normal neurologic outcome is now expected. Future therapies will target specific immune manipulations in the pregnant patient.

The effects of anaemia as a programming agent in the fetal heart

The intrauterine environment plays a powerful role in determining the life-long risk of cardiovascular disease. A number of stressors are well known to affect the development of the cardiovascular system in utero including over/under maternal nutrition, excess glucocorticoid and chronic hypoxia. Chronic fetal anaemia in sheep is a complex stressor that alters cardiac loading conditions, causes hypoxic stress and stimulates large changes in flow to specific tissues, including large increases in resting coronary blood flow and conductance. Decreased viscosity can account for approximately half of the increased flow. It appears that immature hearts are 'plastic' in that increases in coronary conductance with fetal anaemia persist into adulthood even if the anaemia is corrected before birth. These large changes in conductance are possible only through extensive remodelling of the coronary tree. Adult hearts that were once anaemic in utero are more resistant to hypoxic stress as adults but it is not known whether such an adaptation would be deleterious in later life. These studies indicate the need for investigation into the basic mechanisms of coronary tree remodelling in the immature myocardium. New information on these mechanisms is likely to lead to better prevention of and therapies for adult-onset coronary disease.

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.

Predicting the severity of fetal anemia using time-domain measurement of volume flow in the fetal aorta

OBJECTIVES

To assess the value of fetal aortic time-domain measurement of volume flow (using color velocity imaging quantification (CVI-Q)) in predicting the severity of fetal anemia.

METHODS

This was a prospective observational study, in which 24 pregnant women with suspected fetal anemia due to rising anti-red blood cell antibody titers underwent cordocentesis. The fetal aortic time-domain volume flow was measured before fetal blood sampling for fetal hemoglobin investigation. We examined the correlation between increased fetal aortic time-domain volume flow (>2 SD for gestational age) and fetal anemia (hemoglobin level <2 SD for gestational age).

RESULTS

Seventeen fetuses had anemia, and seven had normal hemoglobin. There was a strong correlation between the increase in fetal aortic time-domain volume flow and the drop in hemoglobin value (r = 0.81; P < 0.01). The sensitivity of this technique to predict fetal anemia was 81.3% and the specificity was 71.4%. The mean increase over time in aortic CVI-Q in anemic fetuses was 323.2 mL/min (95% CI, 200.1 to 446.4) compared with 86.9 mL/min (95% CI, -17.7 to 191.5) in the non-anemic group (P = 0.004).

CONCLUSION

Fetal aortic time-domain measurement of volume flow is significantly increased in cases of fetal anemia due to red-cell alloimmunization. These findings can be used to improve the sensitivity, specificity and positive predictive value of the non-invasive techniques used to predict fetal anemia, and may help in the selection of pregnancies that require cordocentesis and transfusion.

Fetal Doppler velocimetry

The introduction of new techniques for evaluating fetal status, particularly fetuses at theoretical risk for hypoxic ischemic encephalopathy, requires the most rigorous evaluation before widespread clinical deployment. The considerations extend beyond clinical value to the significant medicolegal implications of a failure to predict or ascertain compromise. The attitudes to clinical Doppler velocimetry have been shaped to a large extent by these practical concerns and the initial skepticism, which is a necessary component of scientific rigor. Available data strongly indicate, however, that in competent hands umbilical artery Doppler im-proves the clinical management of IUGR pregnancies. Failure to use Doppler may have the undesirable effect of increasing the risk of adverse outcome in the growth-restricted fetus. There is also strong evidence of benefit in the management of the Rh isoimmunization. Although numerous other clinical applications are on the horizon, much more information is needed to determine objectively the benefits and risks of these newer applications.

Evaluation of fetal cardiac contractility by two-dimensional ultrasonography

OBJECTIVE

Evaluation of fetal cardiac contractility by two-dimensional ultrasonography and construction of nomograms of area shortening fraction, end-diastolic area and end-systolic area of fetal cardiac ventricles during uncomplicated pregnancy.

MATERIALS AND METHODS

Fetal echocardiography was performed on 160 pregnant women between 14 and 28 weeks' gestation. Measurements were taken on the four-chamber view. The area of each ventricle was measured by tracing the endocardium at the end of systole and at the end of diastole. Area shortening fraction was calculated by the following formula: SF = (Ad - As)/Ad (SF--area shortening fraction, Ad--end-diastolic ventricular area, As--end-systolic ventricular area).

RESULTS

A statistically significant increase in normal fetal area shortening fraction, end-diastolic area and end-systolic area of both ventricles with advancing gestational age was established. There were no significant differences in the area shortening fraction between right and left ventricles.

CONCLUSIONS

Area shortening fraction shows good correlation with gestational age. Nomogram of area shortening fraction, end-diastolic area and end-systolic area of both ventricles can be used as the reference for evaluation of ventricle size and cardiac contractility in normal and pathological cases.

Splenic artery Doppler peak systolic velocity predicts severe fetal anemia in rhesus disease

OBJECTIVE

We sought to determine whether main splenic artery Doppler peak systolic velocity predicts severe anemia in the rhesus-alloimmunized fetus.

STUDY DESIGN

Splenic artery Doppler peak systolic velocity was obtained before cordocentesis in rhesus-alloimmunized fetuses. Normative values for mean peak systolic velocity based on gestational age were obtained cross-sectionally from a separate group of 144 normal fetuses. The peak systolic velocity values in the study group were expressed as multiples of the median for gestation, and threshold values were used as a screening test for severe anemia. The hemoglobin deficit was defined as mean hemoglobin for gestation minus measured hemoglobin. A hemoglobin deficit value of > or =5 g/dL was used to define severe anemia. We used the peak systolic velocity to screen for severe anemia in the overall study group and the subgroups with or without prior transfusions.

RESULTS

The study population consisted of 26 singleton nonhydropic fetuses in which cordocentesis and Doppler measurements were performed on a total of 55 occasions. The mean gestational age and standard deviation at cordocentesis was 29.6 +/- 4.0 weeks. Severe anemia was noted in 20% of fetal cord blood specimens obtained. On the basis of a receiver operating characteristic curve, a peak systolic velocity of > or =1.4 multiples of the median had a detection rate of 100%, with a false-positive rate of 20.8% in the subgroup with no prior transfusion (relative risk, 4.8; 95% confidence interval, 2.2-10.5). For peak systolic velocity threshold of > or =1.50 multiples of the median, corresponding values in the group with one prior transfusion were 80% and 12.5%, respectively (relative risk, 2.5; 95% confidence interval, 1.2-5.3). There was no risk of severe anemia with a peak systolic velocity below the median for gestation.

CONCLUSION

Fetal hydrops is rare, with a hemoglobin deficit of <5 g/dL. In the first such report the main splenic artery peak systolic velocity was noted to be a strong predictor of severe anemia. For the overall population, all such instances could be diagnosed while cordocentesis was performed 22.7% of the time. There is no risk of severe anemia with Doppler peak systolic velocities below the median for gestational age. The measurement is easily obtained and should be investigated as a clinical tool for minimizing the necessity for cordocentesis.

Sonographic methods to detect fetal anemia in red blood cell alloimmunization

Published reports, case studies, and articles from the English language regarding ultrasonographic detection of fetal anemia in red blood cell alloimmunization were obtained from a MEDLINE search from 1966 to November 1999 using the keywords Rh disease, hemolytic disease of the newborn, ultrasound, and Doppler flow studies and combinations thereof. All articles were cross-referenced. Ultrasound techniques including early findings associated with immune hydrops fetalis, multiple morphologic ultrasound markers, and Doppler flow studies that have been used to detect fetal anemia are reviewed and critically evaluated. Noninvasive sonographic techniques may reduce the number of invasive procedures that traditionally are used to follow fetuses at risk for anemia and decrease the associated risks from these procedures.

Left ventricular hemodynamics in anemic fetal lambs

OBJECTIVE

To assess the left ventricular determinants of cardiac output in 12 chronically instrumented fetal lambs, six of which where made anemic.

METHODS

Twelve, singleton pregnant ewes were instrumented between 123-126 days gestation and chronic catheters placed in-situ. In six fetal lambs, isovolemic fetal anemia was induced (reducing the hematocrit from a mean of 35% to 20%). In a prospective study, absolute 'beat-to-beat' LV volumes and pressures were obtained (gestational age 131-134 days) using a conductance catheter method and a comparison made with non-anemic fetal lambs.

RESULTS

The group of anemic fetuses (n = 6) had a significantly reduced hematocrit as compared to the control group (37% decrease: mean difference--13.4%; P < 0.001). The arterial blood gases of the two groups were not statistically different, with the exception of the pO2 and oxygen content which were significantly lower in the anemic group (P < 0.05). There was no significant change in fetal heart rate, LV preload (as assessed by venous pressure, end-diastolic volume and pressure) or mean arterial pressure between the anemic and control groups. However, a 75% increase in LV stroke volume was observed in the anemic fetal lambs (P < 0.05), secondary to a 61% fall in LV afterload (P < 0.05). There was no significant change in inherent myocardial contractility of the LV, although this did increase to approach statistical significance in the anemic group (P = 0.056). The diastolic time interval was increased by 22% in the anemic fetus, possibly allowing prolonged LV filling time. The indices measuring LV relaxation (Tau and dP/dtmin) were not significantly different in either group.

CONCLUSIONS

This is the first study to report absolute left ventricular volumes in the anemic ovine fetus and the relationship of these data to LV pressure during the cardiac cycle. The model used produces a state of moderately severe, non-hydropic, isovolemic, fetal anemia consistent with those previously described. Although the anemic state was not prolonged, an observed increase in LV stroke volume (which is predominantly due to a decrease in afterload) has been described.

The disappearance of fetal and donor red blood cells in alloimmunised pregnancies: a reappraisal

OBJECTIVE

To determine the proportional reduction per day in the number of fetal and donor red blood cells from the fetal circulation after intrauterine intravascular transfusions.

DESIGN

A retrospective study of 302 transfusions in 101 fetuses.

SETTING

The Department of Obstetrics and Gynaecology of the University Medical Centre Leiden, The Netherlands.

METHODS

We measured the haematocrit in fetal samples both before and after repeated intravascular intrauterine transfusion in fetuses with alloimmune disease. The percentage of fetal erythrocytes was determined in Kleihauer-Betke stained smears. The decline of fetal, donor and mixed red blood cells was calculated by dividing the proportional decrease of the haematocrit values of the number of days between transfusions, also after correction for changes in fetoplacental volumes. Results (given as mean [SD]) are derived from the proportional changes of haematocrit per day.

RESULTS

The interval between the first and second transfusion (15.5 days [SD 5.2]) was shorter than between subsequent transfusions (means ranging from 21.4 to 21.9 days; P < or = 0.0001). The decline per day of mixed, and of donor red blood cells, calculated without corrections for volume changes did not differ from those corrected for volume changes resulting from the transfusion and from fetal growth (correction factor 1.1 [SD 0.4]). Since the coefficient of variance is smaller for the uncorrected decline values, this type of calculation is preferable for clinical purposes. The disappearance of fetal erythrocytes after the first transfusion (6.1%/day [SD 2.9]) was faster than that of mixed fetal and donor red blood cells (3.2%/day [SD 1.2]; P < 0.0001) and of donor cells alone (1.4%/day [SD 1.6]; P < 0.0001). The decline of the mixed red blood cell population became the same as that of the donor cells (2.2%/day [SD 0.8]) after the second transfusion. This decline of donor cells was higher than after the first transfusion (1.4%/day [SD 1.6]; P < 0.05). After the first transfusion the fetal erythrocytes disappeared faster after transplacental puncture of the umbilical cord (6.6%/day [SD 2.8]) than after transamniotic punctures (5.4%/day [SD 2.7]; P = 0.05). The mixed red blood cell also decreased faster (3.5%/day [SD 1.3] versus 2.8%/day [SD 0.9]; P < 0.01).

CONCLUSION

The fast disappearance of fetal erythrocytes, especially after transplacental punctures, shows that the interval between the first and second transfusion needs to be shorter than that for intervals between subsequent transfusions. The number of donor erythrocytes declines by approximately 2% per day.

Right ventricular function in chronically anemic fetal lambs

OBJECTIVE

Our purpose was to determine whether the increase in extravascular fluid in chronic fetal anemia occurs either because of heart failure or despite successful cardiac adaptation.

STUDY DESIGN

Right ventricular function curves were obtained in five ovine fetuses at the start, midpoint, and end of 5 to 8 days of anemia induced by isovolemic daily hemorrhage. Least-squares fit of the ascending and plateau lines of stroke volume versus right atrial pressure were used to establish breakpoints (intersection of the ascending and plateau lines), which were compared by analysis of variance for repeated measures. Myocardial blood flow was measured by microspheres.

RESULTS

Carotid arterial oxygen content was reduced from 7.0 +/- 0.3 to 2.1 +/- 0.1 ml/dl and the hematocrit from 29% +/- 1.8% to 13% +/- 0.6%. Breakpoint analysis of function curves showed that although right atrial pressure remained unchanged (3.4 +/- 0.7 and 3.6 +/- 0.6 mm Hg) stroke volume increased from 1.03 +/- 0.14 to 1.62 +/- 0.25 ml/kg. Both right and left ventricular coronary blood flow were increased, 1351 +/- 313 and 1166 +/- 264 ml/min per 100 gm. Excess fluid was present in abdomen and chest of most animals at autopsy.

CONCLUSION

Tissue edema during severe anemia occurs despite normal right atrial pressure, increased stroke volume, and markedly increased coronary blood flow, markers of successful cardiac adaptation.

Changes in hemorheology with fetal intravascular transfusion

OBJECTIVE

Our aim was to determine the changes in fetal hemorheologic parameters caused by fetal intravascular transfusion for alloimmune anemia.

STUDY DESIGN

Fetal blood samples were collected before and after 95 fetal transfusions in 31 women. Fetal hematocrit, whole-blood viscosity at a variety of shear rates, plasma viscosity, fetal fibrinogen, and fetal plasma proteins were measured.

RESULTS

Fetal whole-blood viscosity increased, sometimes massively, with transfusion. The rise in viscosity was principally dependent on the rise in hematocrit, with a linear rise in hematocrit producing a linear rise in the logarithm of whole-blood viscosity, but was also affected by the amount of adult plasma proteins present in the donor blood.

CONCLUSIONS

Rises in fetal whole-blood viscosity during transfusion can be minimized by using donor blood that has been serum depleted to a high hematocrit (> 90%) and by restricting the end hematocrit to 50% to 55%.

Doppler velocimetry in pregnancy

Since the late 1970s, Doppler velocimetry has been investigated extensively for use in obstetrics. Initially, this technique showed promise for the management of certain complications of pregnancy; this promise has yet to be fulfilled. Doppler velocimetry of either the uterine or umbilical vessels, which showed some merit in selecting growth-retarded fetuses at particular risk, has neither become a screening tool for intrauterine growth retardation nor proven clinically successful in improving fetal outcome. Likewise, its use for other complications of pregnancy (eg, postdate pregnancy, twin pregnancy, and diabetes) has not led to improved pregnancy outcome. More recently this technique has been used to study other vascular beds. Changes in the Doppler characteristics of these vascular beds may demonstrate the fetal response to its environment. These investigations provide the potential for a better understanding of fetal physiology; however, it has yet to be shown by prospective evaluation that their application results in improved pregnancy outcome. This review defines the uses and limitations of Doppler ultrasound in current obstetric practice.

Mathematical modeling of the human fetal arterial blood circulation

A mathematical model of the human fetal arterial circulation based on mass and momentum conservation for one-dimensional flow is presented. We simplified the fetal arterial vascular system from the heart to the placenta, defined 16 anatomical segments and studied the characteristics of the vascular system in relation to changes in morphology and hemodynamics. The two-step Lax-Wendroff finite difference scheme was used to solve the system of equations, after introducing the rheological constants, the diameter and length of the segments measured by two-dimensional imaging and the mean arterial velocity at the inlet segments obtained by pulsed Doppler. The model was validated by comparing the numerical results to our non-invasive ultrasound direct measurements and to previous published data.

Effects of intravascular fetal blood transfusion on fetal intracardiac Doppler velocity waveforms

In 12 fetuses from pregnancies with red blood cell isoimmunization Doppler velocity waveforms were recorded at the level of atrioventricular valves immediately before and at 15-minute intervals for 2 hours after the intravascular transfusion. The left and right cardiac outputs, the ratio between the peak velocities during early passive ventricular filling and active atrial filling at the level of both ventricles as well as the heart rate were calculated. Before transfusion, the left and right cardiac outputs were significantly higher than reference ranges for gestation that were constructed from the cross-sectional study of 187 normal pregnancies. After transfusion there was a significant temporary fall in right and left outputs associated with increased ratios between the peak velocities during early passive ventricular filling and active atrial filling. Within 2 hours after transfusion both parameters returned toward the normal range. In addition, no significant changes were found for fetal heart rate values before and after transfusion. The fall of cardiac output was significantly related to the amount of expansion of the feto-placental volume.

Acute fetal hemodynamic alterations after intrauterine transfusion for treatment of severe red blood cell alloimmunization

One of the compensatory hemodynamic mechanisms seen in the anemic human fetus is an increased cardiac output. With Doppler techniques, cardiac output was measured in 21 fetuses before and immediately after 38 intrauterine transfusions for severe red cell alloimmunization. Umbilical venous pressures were measured before and after transfusion; amniotic fluid pressure was also quantitated. After subtraction of amniotic pressure, umbilical venous pressure increased by 1.7 +/- 2.8 mm Hg (p less than 0.01). Left and right ventricular output declined by 19% and 22%, respectively (p less than 0.001). Four factors are known to affect cardiac output: heart rate, cardiac contractility, preload, and afterload. Fetal heart rate and mean acceleration, a measure of myocardial contractility, were unchanged after transfusion. A calculated mean increase in the fetoplacental volume of 18% in conjunction with an increase in umbilical venous pressure would indicate that cardiac preload was increased. We propose that intravascular intrauterine transfusion leads to an increased cardiac afterload, possibly by increasing blood viscosity. The fetal heart responds to the increased afterload by a decrease in stroke volume, leading to a fall in cardiac output.

Effects of behavioural states on cardiac output in the healthy human fetus at 36-38 weeks of gestation

Doppler velocity waveforms from atrioventricular valves were recorded in 20 healthy fetuses at 36--38 weeks of gestation during both behavioural states 1F (quiet sleep) and 2F (active sleep). No significant changes were found in the ratios between the velocities during early passive ventricular filling and active ventricular filling (E/A ratios) at the level of both mitral and tricuspid valves when the measurements obtained during states 1F and 2F were compared. Moreover, during state 2F the left ventricular output increased and the right ventricular output decreased, resulting in a marked modification of the right to left cardiac output ratio. Our data suggest a redistribution of cardiac output in favour of the left side of the heart during state 2F.