Chapter 482. Fetal Cardiology

The origins of fetal cardiology were in the novel and still relevant fetal lamb investigations of Rudolph and Heymann.1-3 From these early studies we began to understand normal fetal cardiovascular physiology and developed hypotheses regarding the evolution of congenital heart disease (CHD) in utero and its influence on fetal circulation.4 With advances in ultrasound technology in the late 1970s and 1980s, it became possible to demonstrate normal fetal cardiac anatomy and document growth of the cardiac chambers and great arteries.5-9 Doppler investigations in the 1980s and 1990s added insight into developmental changes in normal human fetal circulation and cardiovascular function.10-13 Initial reports describing prenatal detection of fetal CHD documented a more severe spectrum of disease than that encountered after birth.14-16 This was at least in part a consequence of the ease with which the more severe pathology, including fetal hydrops, was recognized at routine ultrasound assessment.

Advances in ultrasound technology over the past 20 years have led to monumental improvements in our ability to define fetal cardiovascular anatomy and to evaluate normal and altered myocardial function in greater detail.To date, most forms of CHD, both major and minor, have been detected prenatally. It has even become possible to define fetal cardiovascular anatomy and function and to detect abnormalities of cardiovascular structure, function, and rhythm as early as 10 to 14 weeks of gestation, only a short time after completion of cardiac morphogenesis. With rapid advances in technology, fetal cardiology has evolved as its own subspecialty that merges maternal-fetal medicine and pediatric cardiology. This chapter reviews unique aspects of this field and its role in the management of neonates with significant structural and functional CHD.

Pregnancies at increased risk for fetal congenital heart disease (CHD), whether structural, functional, or rhythm related, are evaluated by the fetal echocardiogram. Indications for fetal echocardiography include maternal diseases associated with fetal CHD (eg, maternal diabetes, phenylketonuria, and autoimmune pathology), maternal infection, and maternal exposure to medications known to be teratogenic for the developing fetal heart. Fetal indications include a suspected cardiac abnormality at routine ultrasound; a suspected extracardiac abnormality in the fetus, including a chromosomal abnormality known to be associated with CHD; an abnormal fetal rhythm; and conditions associated with altered fetal heart function (eg, twin-twin transfusion syndrome, acardiac twins, anemia). A family history of CHD (mother, father, or sibling) or of a syndrome associated with CHD are also indications. Although many pregnancies are referred as a consequence of maternal disease or a family history of CHD, the majority of positive referrals (pregnancies with fetal CHD) come from the low-risk population and are referred because of a suspicion of CHD during routine ultrasound assessment.17-18 Recognition of this has prompted educational initiatives to train obstetrical ultrasound personnel for better screening of the heart at the time of routine obstetrical scanning.

Pregnancies at risk for fetal CHD as a consequence of a known family history and maternal disease are often referred electively for fetal echocardiography at 17 to 23 weeks of gestation, prior to the gestational age limit for elective pregnancy termination in most North American practices. Many pregnancies with fetal CHD and extracardiac pathology are identified at the time of routine fetal ultrasound and are referred in a timely fashion. There has been an increasing interest in earlier fetal diagnosis, with reports of cardiac pathology identified as early as the late first and early second trimesters.19-25 This has been at least in part facilitated by the advent of fetal nuchal translucency assessment at 11 to 14 weeks. Increased fetal nuchal translucency at 11 to 14 weeks of gestation is observed in trisomy 21 and other aneuploidies,26 conditions associated with structural and functional fetal CHD. In the absence of aneuploidy, increased fetal nuchal translucency is associated with a broad spectrum of structural and functional fetal CHDs, occurring in 2% to 9% of affected pregnancies with an exponentially increasing risk, the greater the nuchal translucency.25,27 Although not yet used in clinical practice, fetal Doppler interrogation has the potential to provide insight into normal first trimester fetal cardiovascular function28-29 and its relationship with fetal viability.29

Fetal echocardiography is best performed by a fetal cardiologist trained in pediatric echocardiography with additional experience in fetal diagnosis and management. The assessment includes detailed two-dimensional imaging of cardiac and vascular structures (eFig. 482.1) and spectral and color Doppler interrogation (eFig. 482.2).30 Fetal imaging represents a challenge because the pediatric echocardiographer must image the fetus through the maternal abdomen. Orientation to the position of the fetus within the maternal uterus, including left and right sides, head and feet, and anterior and posterior aspects of the fetus, are a critical first step in obtaining decipherable images. Limited maternal acoustic windows, suboptimal fetal position, and the diminutive size of fetal cardiac structures contribute to difficulty in scanning. Once the assessment is complete, the fetal cardiologist must be able to interpret the pathology and provide accurate counseling to the anxious pregnant woman and her partner.

Most major and even minor structural CHDs can be detected before birth.31 In the hands of an experienced echocardiographer, the fetal echocardiogram can yield significant anatomic detail regarding the cardiovascular pathology, similar to that obtained after birth.32-34 The segmental anatomy, including visceral and atrial situs, systemic and pulmonary venous connections, ventricular morphology, ventricular and great artery connections, and ductus arteriosus and aortic arch morphology, are typically defined, and blood flow is demonstrated in each structure by pulsed and color Doppler. Despite the accuracy of fetal echocardiography, there are limitations in image resolution that result in an inability to define all the anatomy. Small to moderate-sized atrial and ventricular septal defects, minor valve abnormalities, and isolated pulmonary vein and coronary artery abnormalities may not be detected at fetal echocardiography. Unique aspects of the fetal circulation including the presence of fetal shunts (the foramen ovale and ductus arteriosus, which permit a redistribution of flow and equalization of pressures) and the role of the placenta and the ductus venosus are considered in the interpretation of the findings. For instance, discrepancy in ventricular or great artery size suggests left or right ventricular heart obstruction, despite the absence of detectable gradients. Retrograde flow in the ductus arteriosus or aortic arch indicates critical pulmonary or aortic outflow tract obstruction, respectively.35 Evaluating fetal structural CHD requires consideration of what can complicate the prenatal and postnatal outcome of an affected fetus, including additional structural or functional cardiac pathology, some of which may not be evident on the first evaluation but may progress later in gestation or only manifest after birth.

Structural CHD most frequently detected before birth includes lesions associated with an abnormal four-chamber view or lesions associated with significant extracardiac pathology, all of which may be detected at routine fetal ultrasound screening.17,18,31,36,37 Hypoplastic left heart syndrome, one of the most common critical neonatal heart lesions, is one of the more commonly diagnosed fetal CHDs.31,36,38-41 In many centers, more than 50% of affected fetuses are identified before birth. Its recognition is facilitated by the obvious abnormality in the four chambers (Fig. 482-1). In contrast, tetralogy of Fallot, another commonly detected form of fetal CHD, is not associated with an abnormal four-chamber view other than levorotation of the heart,42 and its detection in isolation requires recognition of the outflow tract and great artery abnormalities (Fig. 482-2). It is, however, frequently associated with chromosomal abnormalities, including aneuploidy and 22q11.2 deletion (Di George syndrome) and extracardiac structural pathology including renal, gastrointestinal, and limb anomalies,37,38 which findings may prompt referral for fetal echocardiography.

Most structural CHD in the fetus has the potential to evolve prenatally, necessitating serial evaluation during the pregnancy (Table 482-1).43 Mechanisms of progression usually involve development of more severe disease, structural, functional, or both. Left and right heart obstructive lesions including semilunar and atrioventricular valve obstruction are among the fetal CHDs with the greatest potential to evolve. Critical aortic or pulmonary stenosis in the mid-trimester, for instance, leads to left or right ventricular hypertrophy, respectively, and eventual dysfunction.44-47 As long as the function of the unobstructed ventricle is not affected, blood is redistributed toward that ventricle, which provides the equivalent of a biventricular output. If this is a gradual process, the single functioning ventricle can sustain this additional output without decompensation (the combined ventricular output in the fetus is about 450 to 500 mL/kg/min).1,3,12 That this is well tolerated is not surprising because the heart at delivery, with the change to in series circulation and the increased metabolic demands associated with breathing and thermoregulation, ejects a combined ventricular output of about 800 mL/kg/min. With a redistribution of flow, there is diminished filling of the obstructed ventricle and, with time, progressive hypoplasia of that side of the heart including the atrioventricular and semilunar valves, the ventricle, and the great artery. The aortic arch or ductus arteriosus provides blood flow to the fetal body with retrograde filling of the vessel distal to the obstruction, either the pulmonary arteries in critical pulmonary stenosis or to the ascending aorta in critical aortic stenosis. More rapid evolution of ventricular dysfunction, or significant atrioventricular valve regurgitation, when both ventricles are compromised, may lead to fetal heart failure and even demise.

To prevent disease progression, invasive fetal cardiovascular procedures have been attempted directed largely at ameliorating the less severe lesion early in its course. There may be abnormalities of the fetal circulation that result in progressive fetal cardiovascular pathology, most commonly fetal heart failure, including constriction of the ductus arteriosus, which may occur in the second and third trimesters,52-53 foramen ovale restriction,54 and even absence of the ductus venosus,55 a condition associated with a progressive high cardiac output state. Knowledge of the potential for evolution is critical in prenatal counseling and perinatal management of affected pregnancies. To date, successful balloon dilation of the fetal aortic and pulmonary valve have been described48-50 (Fig. 482-3). Atrial septostomy and even stent placement have also been described in fetuses with hypoplastic left heart syndrome and restrictive atrial communication.51 Issues around patient selection, optimal timing of intervention, and technical aspects of the procedures are still evolving.

Once a diagnosis of fetal congenital heart disease (CHD) is made, the fetal cardiologist counsels the pregnant woman and her partner regarding the diagnosis, the potential for evolution, associated morbidity, and when appropriate, need for additional testing. The counseling usually takes into account the additional cardiovascular lesions that may or may not be detectable but that can affect the clinical course. A postnatal algorithm of clinical outcome and management may be presented for lesions in which the severity of pathology and postnatal clinical picture is not entirely predictable. The potential for extracardiac pathology must be considered in the counseling. Fetal CHD is often associated both with chromosomal abnormalities and extracardiac structural pathology that may not only affect the clinical course of the fetus, but may not be recognized prenatally. The incidence of aneuploidy, for instance, in fetal CHD ranges from 15% to 25%, depending upon the series and the type of fetal CHD.36,37,56,57 For certain forms of CHD, chromosomal abnormalities are common, including conotruncal lesions (eg, tetralogy of Fallot, truncus arteriosus, double outlet right ventricle) and coarctation of the aorta, whereas other CHDs, including complete transposition of the great arteries and that associated with heterotaxy syndrome, have a lower risk. These relative risks must be incorporated into the decision regarding chorionic villous sampling or amniocentesis. Depending upon the timing of diagnosis, the fetal cardiologist and obstetrical staff provide options available to the pregnant mother with respect to continuation of the pregnancy. For more severe cardiovascular lesions or a combination of cardiovascular and extracardiac pathology associated with high risk of fetal and neonatal compromise and with a more guarded prognosis, discussions regarding aggressive prenatal and neonatal management are necessary. For very severe pathologies, planned compassionate perinatal and neonatal care may be chosen.58 Such discussions ideally involve personnel from all of the disciplines caring for the pregnant mother and infant to avoid unnecessary confusion or inappropriate management of both mother and fetus.

Fetal Arrhythmias

Echocardiographic Diagnosis of Fetal Arrhythmias

Fetal cardiac arrhythmias have been noted in up to 5% of all pregnancies.59 Fortunately, the vast majority are benign and are largely premature atrial beats, commonly found in the third trimester. Occasionally a more serious or persistent fetal arrhythmia is present. Pregnant mothers usually are referred for persistent fetal tachycardia (heart rate > 170 bpm), bradycardia (heart rate < 110 bpm) or irregular rhythm, as detected by a Doppler listening device. The mechanism of the fetal arrhythmia is deciphered by fetal echocardiography by assessing the temporal relationships of atrial and ventricular contraction. M mode with placement of the cursor through one of the atria (usually the right) and either left or right ventricle demonstrates wall motion of the chambers (Fig. 482-4). Simultaneous pulsed Doppler interrogation of left ventricular inflow and outflow, superior vena caval and ascending aortic flow, or pulmonary venous and pulmonary artery flow permit an indirect evaluation of the relationship between atrial and ventricular contraction (Fig. 482-4). Although fetal electrocardiography and magnetocardiography have permitted more definitive evaluation of fetal heart rhythm, lack of availability and technical limitations have prevented more widespread use in clinical practice.60-62 Most types of arrhythmia detected in the pediatric population have also been identified before birth. eTable 482.1 lists the types of arrhythmias that have been diagnosed prenatally.

Fetal Tachycardias

Atrial and ventricular ectopy with isolated extrasystoles are usually benign. Ventricular tachycardia is very rare but can occur with myocardial disease or intracardiac tumors. Premature atrial beats detected in the fetus in 2% of pregnancies are associated with intermittent supraventricular tachyarrhythmia. The two most common forms of fetal tachycardia are supraventricular tachycardia, usually associated with an accessory ventricular-atrial pathway, and atrial flutter (Fig. 482-5). In recent years, fetal cardiologists have made a greater effort to define the mechanisms of these tachyarrhythmias, resulting in more accurate counseling and more effective treatment strategies.63-64 Tissue Doppler, which uses Doppler shifts of the myocardium using very high sampling rates and with postprocessing capabilities, may ultimately facilitate definition of arrhythmia mechanism.65

Fetal supraventricular tachyarrhythmias can be associated with fetal heart failure, likely caused by reduced filling time and secondary increases in central venous pressures. Elevated central venous pressure not only affects umbilical venous return and leads to placental edema and dysfunction, but it may also impair liver function, leading to reduced serum protein production. This accelerates the evolution of effusions and skin edema. Based on the findings of a recent experimental animal model, altered systolic and diastolic function in fetal tachycardia may also be related to the rapid utilization of glycogen stores.66,67 When fetal hydrops is present, the morbidity and mortality associated with fetal supraventricular tachycardia ranges from 23% to 50%. Even after conversion to sinus rhythm, fetal supraventricular tachyarrhythmias with hydrops are associated with a 10% loss rate.68 Cerebral vascular events have also been reported in fetal supraventricular tachyarrhythmias and hydrops.69 Given these observations, maternal/transplacental antiarrhythmia therapy is often initiated before the evolution of gross fetal cardiovascular compromise. Risk factors for the evolution of heart failure include incessant tachycardia, presentation prior to 32 weeks, tachycardia > 230 bpm, and structural heart disease (eg, Ebstein anomaly).70 Maternal administration of digoxin has been the antiarrhythmic medication used most widely in the treatment of fetal supraventricular tachyarrhythmias, with success (absence of hydrops) reported in 32% to 71% of treated pregnancies.71-73 Placental transfer of digoxin, however, is significantly reduced when placental edema is present, resulting in inadequate treatment of affected fetuses.73,74 In addition, digoxin is usually not effective therapy for atrial flutter and less common forms of supraventricular tachycardia, including ectopic atrial tachycardia and permanent reciprocating junctional tachycardia.75,76 As a consequence, More potent antiarrhythmics including sotalol, flecainide, amiodarone, propranolol, and procainamide have been employed.59,64,68,71-73,77-85 As is true postnatally, no one medication has been uniformly effective for fetal supraventricular tachycardia, and most of these medications have important side effects, including potential to cause more serious arrhythmias in both mother and fetus. The mothers are usually monitored closely and even hospitalized when more potent antiarrhythmic medications are used until a therapeutic dose is tested. Maternal-placental antiarrhythmic therapy for fetal supraventricular tachycardia is very successful with conversion in up to 85% of affected fetuses.78 Success rates of as high as 80% have been reported in the presence of fetal hydrops, although this typically requires the use of more than one medication and may take longer to achieve.71-73,78-80,85 Rarely, intraumbilical or intramuscular delivery of an antiarrhythmic medication for refractory fetal supraventricular tachycardia may be necessary.86,87

Fetal Bradycardias

The most common form of fetal bradycardia is sinus bradycardia, typically associated with a gradual slowing of the fetal heart rate and rapid resolution. Persistent fetal bradycardia is more worrisome because it may be due to fetal atrioventricular block (Fig. 482-5). Fetal atrioventricular block may be associated with certain structural CHD, including left atrial isomerism (polysplenia syndrome) and L-transposition of the great arteries.88-90 It is also observed in pregnant mothers with autoantibodies anti SSA-Ro and SSB-La89-92 in the absence of structural fetal heart disease, and, in the neonate, is one component of the clinical picture referred to as “neonatal lupus erythematosus.”93 These autoantibodies are observed in autoimmune disease such as systemic lupus erythematosus and Sjogren syndrome, but also occur in the absence of clinical autoimmune disease, a more common finding in mothers of affected fetuses.91,92 Fifteen to twenty percent of fetuses with maternal autoimmune-mediated atrioventricular block can develop more diffuse myocardial disease. Clinical myocardial dysfunction places them at high risk of mortality and morbidity.92,94-96 Myocardial disease may even be observed in the absence of atrioventricular block.97 Without myocardial disease, the clinical outcome of fetuses with autoimmune-mediated AV block is generally good with a greater than 85% survival94,98 and may be at least in part attributed to the use of maternal corticosteroids and sympathomimetics, and to improved perinatal and postnatal management of affected infants.94 In contrast, the clinical outcome of atrioventricular block and structural CHD is very poor, particularly in left atrial isomerism which can present very early in gestation and be associated with very low, monotonous ventricular rates.88-90

Fetal Heart Failure

In the fetal circulation, blood is oxygenated in the placenta and returns through the umbilical vein to the fetal cardiovascular system. Typically, in the normal fetus, undulations in umbilical venous blood flow of low velocity typically occur only during fetal breathing.99 Umbilical venous return requires low downstream central venous pressures. Any cardiovascular or extracardiac abnormality that alters these pressures can compromise umbilical venous return and lead to fetal hypoxemia and placental edema. Fetal lymphatic flow is significantly higher than that of the newborn and the adult.100,101 Thus, small changes in ventricular and consequent central venous pressures can reduce lymphatic flow and lead to fetal edema, the manifestation of cardiac failure. Much like the clinical picture of right heart failure observed after birth, fetal heart failure is associated with the evolution of ascites, pleural and pericardial effusions, and skin edema (Fig. 482-6). In its most severe state, with two or more fluid-filled cavities, fetal heart failure is referred to as hydrops fetalis. In addition to the fetal-placental circulation and the unique nature of the fetal lymphatics, other factors that place the fetus at higher risk for the development of right heart failure and effusions include high compliance of the interstitial space, high capillary filtration coefficient which allows large water flux at low vascular pressure, low colloidal osmotic pressure, and high capillary permeability.102

The fetal circulation requires that there be at least one patent and competent inflow, one patent and competent outflow, one ventricle that fills normally and can maintain the equivalent of a combined ventricular output, and a well-functioning placenta.103 If there is a problem with any one of these, fetal heart failure and even spontaneous intrauterine demise with or without hydrops can occur. As is true for most fetuses with critical outflow obstruction, severe dysfunction of one ventricle does not usually lead to the evolution of heart failure unless it alters the function of the other ventricle. There are structural cardiac lesions in which abnormal function of one ventricle more consistently leads to altered function of the other. This is particularly true for lesions associated with severe atrioventricular or semilunar valve insufficiency in which significant volume load of one ventricle can alter the ability of the other ventricle to fill. When this occurs, without an ability to redistribute flow toward the “unaffected” ventricle, atrial filling pressures increase, leading to increased central venous pressures. Furthermore, this pathophysiology makes it difficult for the fetus to adjust to acute physiological demands, which may put the fetus at risk for intrauterine fetal demise in the absence of hydrops. These observations have been reported in both Ebstein anomaly of the tricuspid valve and tetralogy of Fallot with absent pulmonary valve syndrome.104,105 Other cardiovascular abnormalities associated with the evolution of fetal hydrops include cardiomyopathies, particularly those associated with altered ventricular filling,106 tachycardias and bradycardias, high cardiac output states, high ventricular afterload as observed in the recipient twin in twin-twin transfusion syndrome,107,108 and extracardiac pathologies that prevent filling of the fetal heart (Table 482-2). For many of these pathologies, fetal echocardiography plays an important role in the assessment of an affected pregnancy, determining optimal time for prenatal interventions, monitoring after prenatal interventions, and planning delivery.

Although the outcome of most hydropic fetuses with cardiovascular pathology is guarded, postnatal survival is possible if the hemodynamic condition can be improved. For example, in pregnancies with fetal hydrops caused by abnormalities of the fetal circulation, including agenesis of the ductus venosus and premature constriction of the ductus arteriosus, delivery can result in rapid improvement in the hemodynamic condition of the infant and survival. In Ebstein anomaly of the tricuspid valve, if there is patency of the pulmonary valve, even with severe tricuspid insufficiency, delivery of the fetus, allowing the ductus arteriosus to close and the pulmonary vascular resistance to fall, may be sufficient to promote forward pulmonary blood flow and decrease tricuspid insufficiency.109 Early pacemaker therapy in the neonate with atrioventricular block and mild or moderate hydrops may result in survival if the structure of the heart is normal or correctable.110 If there is no means of medically or surgically improving the hemodynamic abnormalities that led to the evolution of hydrops before birth, delivery only adds an additional hemodynamic burden associated with the transition from fetal to neonatal circulation and may result in progressive cardiovascular compromise and death.

A multidisciplinary approach to diagnosis, counseling, and perinatal and neonatal management of fetal CHD is an important factor in optimizing the outcome of fetal CHD, particularly when severe. The team consists of an obstetrician or perinatologist as the primary caregiver, a fetal cardiologist, a geneticist, a neonatal specialist, other pediatric and surgical subspecialists (depending upon the cardiac and extracardiac pathology), and supportive services including an experienced perinatal or neonatal social worker.

For most fetal CHD, vaginal delivery as close to term is desired. A mother who lives far away from the tertiary care center may require a scheduled induction of labor to ensure the delivery occurs in the appropriate facility. Rarely, in the most compromised fetuses or when an emergency intervention is needed at the time of delivery, a caesarian section is necessary, and a neonatologist should be available for the resuscitation. Although term delivery is most desired, when there is fetal stress or evolving fetal hydrops, a premature delivery may preferable.

Critical fetal CHD, which requires maintaining ductus arteriosus patency after birth or immediate medical or surgical intervention, warrants a planned delivery in a tertiary/quaternary care center (eTable 482.2), obviating the need to transport the infant to another center, and ensures that the mother and family are nearby.

For lesions of moderate or uncertain severity, and therefore with an uncertain clinical presentation after birth, a more conservative approach with delivery of the infant at the tertiary or quaternary care center is usually considered. Such lesions include isolated coarctation of the aorta, moderate semilunar valve stenosis, and tetralogy of Fallot with anterograde flow through the ductus arteriosus. If the lesion is more severe than expected, the appropriate care can be provided, including medical and surgical intervention. In coarctation of the aorta, for instance, the arch obstruction may not always be severe enough to warrant prostaglandin therapy to maintain ductus arteriosus patency. The neonatal and pediatric cardiology team may choose to perform a hyperoxia test,111 and if the infant passes, observe the infant until the ductus arteriosus has closed to confirm the absence of severe distal arch obstruction and its sequellae. In fetal tetralogy of Fallot, it is difficult to consistently predict the degree of cyanosis that will occur with ductus arteriosus closure after birth.

For minor CHD and fetal CHD not likely to be a problem within the neonatal period (eg, isolated ventricular septal defect, balanced atrioventricular septal defect, and minor valve abnormalities), it may be acceptable for the delivery to occur in a local hospital with pediatric assessment shortly after birth and planned early pediatric cardiology evaluation. This allows the pregnant mother to deliver close to home, in a familiar environment with her primary obstetrician.

The clinical impact of fetal diagnosis has been documented best in structural CHD. Planned management of critical CHD avoids the potential cardiovascular compromise that may acutely evolve as a consequence of ductus arteriosus constriction and may be associated with an improved preoperative condition, with less acidosis and end organ damage, and better postoperative survival,114-118 and long-term myocardial and neurodevelopmental function may also be improved. Prenatal diagnosis with medical intervention has resulted in improved survival in fetal tachyarrhythmias and bradyarrhythmias.69,92,112

Although less emphasized, timely prenatal diagnosis of severe CHD, with subsequent pregnancy termination, has the potential to alter the clinical spectrum of disease observed after birth.119-120 This was first recognized in the United Kingdom in the early 1990s, where, concomitant with increasing rates of prenatal diagnosis of hypoplastic left heart syndrome, a decrease in the number of neonates diagnosed with the condition was observed.119 Even when a pregnancy is continued, prenatal diagnosis also has an important psychological and emotional impact for the pregnant woman and her family, as it provides time to prepare for having an affected child.121

Fetal cardiology has evolved significantly over the past 2 decades. Although there is no question that it has had an important impact in fetal and neonatal medicine, its potential impact is limited by current prenatal detection rates that are still far from desired internationally.122-126 Ongoing efforts to improve prenatal ultrasound screening and even identify more objective and less technician-dependent strategies to improve detection are necessary if fetal cardiology is to achieve its full potential.