Optimizing prenatal detection of congenital heart disease (CHD) is an important clinical goal. Congenital heart disease is a leading cause of perinatal morbidity and mortality, accounting for 20% of perinatal mortality and 50% of infant mortality from congenital anomalies.1 Research shows that prenatal diagnosis of major CHD may improve outcomes compared with postnatal diagnosis.2
Universal screening for CHD is recommended during routine anatomic survey.3 The four-chamber heart view, the most basic assessment of the fetal heart, is often considered the minimum standard for screening. However, reported detection rates with four-chamber heart view vary widely, ranging from 4% to 63%,1,2 with many studies demonstrating disappointing results when using this view alone.4 Some major anomalies, such as conotruncal abnormalities, are not routinely detected by the four-chamber heart view. Visualization of the ventricular outflow tracts may improve detection rates of major CHD to approximately 50%–90%.5 – 8 The American College of Obstetricians and Gynecologists, the American Institute for Ultrasound in Medicine, the International Society of Ultrasound in Obstetrics and Gynecology, and the American College of Radiology each recognize the benefit of including outflow tracts and state that they should be attempted “when technically feasible.”9 – 11
Unfortunately, even with these guidelines and recommendations, a proportion of CHD remains undiagnosed until the neonatal period or later.12 – 14 In a case series by Acherman et al,14 only 14 of 39 outflow tract abnormalities and 12 of 28 atrioventricular septal defects were identified before delivery. Detection rates for obstructive lesions were even lower. As a result, some authors14 have advocated fetal echocardiography for all pregnancies. This approach has yielded high-detection rates, with one study reporting a sensitivity of up to 88.5%, including minor anomalies.15
Whereas detailed fetal echocardiography improves detection rates over routine screening, it is more technically demanding and is associated with increased costs. Most centers refer only a subset of at-risk patients rather than performing fetal echocardiography in an unselected population. Apart from abnormal heart views on anatomy ultrasound scan, common referral indications include maternal diabetes, single umbilical artery, a family history of major CHD, increased nuchal translucency, and chromosomal abnormalities.3,16 The purpose of this study was to estimate the utility of using fetal echocardiography as a second screening test in patients with risk factors for CHD after a normal obstetric screening ultrasound scan.
MATERIALS AND METHODS
After obtaining approval from the New York University School of Medicine Institutional Review Board, the pediatric cardiology database was searched for all fetal echocardiography studies performed between January 2002 and June 2006 at New York University Medical Center, a university-based tertiary care center in New York City. Diagnostic fetal echocardiography is performed by pediatric cardiologists in an ultrasound suite separate from obstetric ultrasonography. This group of patients was cross-referenced with patients who underwent screening ultrasound scans in the Obstetrics and Gynecology Ultrasound Unit at New York University before undergoing fetal echocardiography. Patients who did not have an obstetric screening ultrasound scan at the Obstetrics and Gynecology Ultrasound Unit were excluded. Patients referred for a second-opinion fetal echocardiogram were also excluded.
For patients who met these criteria, we extracted demographic data, gestational age, screening ultrasound findings, and reason for referral to pediatric cardiology (such as risk factors for CHD). The screening examination was classified as having suspicious cardiac views, abnormal extracardiac findings, or no abnormalities. Cardiac views were defined as suspicious if an abnormality was seen or if adequate visualization of the requisite views was suboptimal. Isolated intracardiac echogenic foci are not strongly associated with structural heart disease3,17 and were considered to be normal variants in this study.
The standard practice of the Obstetrics and Gynecology Ultrasound Unit is to perform the anatomic survey at 20–22 weeks of gestation, including the four-chamber heart and outflow tract views. Aortic and ductal arch views are also included in the screening examination. If cardiac views are suboptimal, then a second attempt is made on return visit before referral for fetal echocardiography (if gestational age allows). In addition, an early anomaly screening ultrasound scan is offered at 14–17 weeks of gestation. The protocol of the New York University Pediatric and Fetal Echocardiography Laboratory for performing fetal echocardiography includes evaluation of outflow tracts, a four-chamber view, aortic and ductal arches, valves and septa, pulmonary veins, systemic veins, and functional analysis and flow analysis using Doppler and two-dimensional ultrasonography, all performed from multiple views. The echocardiography protocol fulfills guidelines set forth by the American Society of Echocardiography.16 Because specific protocols for the anatomic survey and fetal echocardiography vary by institution, and to reduce the risk for ascertainment bias, only patients undergoing both studies at NYU were included in this cohort.
Detailed fetal echocardiography reports were reviewed by a single pediatric cardiologist (C.K.L.P.), blinded to referral indication. Echocardiography findings were classified as demonstrating no CHD, minor CHD, or major CHD. A major finding was defined as a diagnosis that would likely necessitate medical or surgical intervention (or both) in the first 6 months of life, whereas a minor finding was defined as a diagnosis unlikely to require such intervention. These definitions are similar to those used in other studies.14
Additionally, neonatal intensive care unit billing logs were used to identify additional patients with major CHD who underwent an anatomy scan in the obstetrics and gynecology unit. Neonates admitted to the neonatal intensive care unit within 1 month of birth with a congenital heart anomaly were identified to determine if they had undergone an anatomy scan in our unit. In this manner, additional cases of major CHD could be reviewed to determine whether the obstetric screening examination failed to detect major CHD and fetal echocardiography (if performed) could have aided in detecting those anomalies prenatally.
Of 1,034 patients in the pediatric cardiology database, 55 patients were excluded because of incomplete data or because they were referred for a second opinion (Fig. 1). The most common indications for referral for echocardiography were family history and diabetes, together accounting for more than 40% of patients (Fig. 2). When cross-referencing the fetal echocardiography database with our obstetric ultrasound database, we identified 536 patients as having undergone an anatomy scan at New York University's Obstetrics and Gynecology Ultrasound Unit. Of these 536 patients, 80 underwent fetal echocardiography for suspicious (abnormal or suboptimal) cardiac views, 139 for extracardiac abnormalities, and 317 had normal results after screening ultrasound scans (Fig. 1). Maternal demographics are presented in Table 1. Overall, the four-chamber heart, outflow tract, and arch views were imaged adequately in 490 of the 536 (91.4%) patients during anatomy ultrasound scan.
Of the 317 patients who had unremarkable screening ultrasound scans, none was found to have major CHD on fetal echocardiography. Twenty-six of 28 (92.9%) cases of major CHD were detected in patients with suspicious cardiac views on anatomy ultrasound scan. The remaining two cases of major CHD were detected in fetuses with extracardiac anomalies (Fig. 3). The most commonly detected type of major CHD was hypoplastic left heart (Table 2).
Of the 317 patients who had normal screening ultrasound results, 31 (9.8%) were found to have minor CHD. The most common minor anomalies found were small ventricular septal defects (59% of minor CHD), tricuspid regurgitation (11%), and small pericardial effusions (9%). Although an early anatomic survey was routinely offered at 14–17 weeks of gestation, the majority of patients (68%) only underwent one examination. Among those who did undergo both examinations, only one case of major CHD was suspected solely based on the second scan. A review of the neonatal intensive care unit billing records and neonatal echocardiography reports identified four additional cases of major CHD that underwent screening ultrasonography in the Obstetrics and Gynecology Ultrasound Unit but were not identified in the pediatric cardiology database.
The first case involved a diagnosis of tetralogy of Fallot that was correctly identified on the obstetric screening ultrasound examination, but the patient with this diagnosis did not undergo fetal echocardiography at our institution.
In the second patient, the obstetric scan did not reveal any suspicious cardiac findings, although an omphalocele was diagnosed. This finding of an extracardiac anomaly prompted referral for fetal echocardiography. The fetal echocardiography report suggested a large foramen ovale, but no anomaly was diagnosed. The newborn, however, was found to have a coarctation of the aorta that was not detected on either the obstetric scan or the fetal echocardiography.
The third case involved a newborn found to have several small atrial and ventricular septal defects that required surgical repair. Although the obstetric scan did not reveal any cardiac findings, a single umbilical artery prompted referral for fetal echocardiography. However, the fetal echocardiography was unremarkable and this challenging diagnosis was unable to be made.
The final patient with major CHD did have an unremarkable obstetric screening examination and, given the absence of other risk factors, was never referred for fetal echocardiography. The newborn was found to have Down syndrome, and neonatal echocardiography showed an atrioventricular canal defect with a small ventricular component. Review of the obstetric scan showed a normal-appearing four-chamber image. Review of the neonatal echocardiogram by the pediatric cardiologist identified a small posterior inlet ventricular septal defect, with several four-chamber heart images appearing entirely normal.
Of note, two major anomalies were detected by virtue of including aortic and ductal arch views in the routine screening examination when the conventional four-chamber and outflow tract views were labeled as normal. In one patient, the suboptimal aortic arch view led to the diagnosis of aortic stenosis and insufficiency with poststenotic dilation of the ascending aorta on fetal echocardiography. Neonatal echocardiography confirmed the diagnosis and found a tri-commissural aortic valve with fused leaflets. In the second patient, a suboptimal aortic arch view in a fetus with a sacrococcygeal teratoma prompted identification of dilated aortic arch on fetal echocardiography and, ultimately, a ventricular septal defect and dilated aorta on neonatal echocardiography. However, given the extracardiac anomaly, this patient would have been referred for fetal echocardiography even in the absence of the suboptimal aortic arch view.
Prenatal diagnosis of major CHD has been shown to improve outcomes and allows for patient counseling and appropriate referral to tertiary care centers.2,18 – 23 Some authors have recommended universal fetal echocardiography because this strategy has demonstrated excellent detection rates for major CHD. In comparison, anatomy ultrasonography has demonstrated varying sensitivities in previous studies.1,4 – 8,14,15 However, extending echocardiography universally would require a considerable commitment of resources. Bahtiyer and Copel24 estimated an increased annual cost at $1.7 billion with universal fetal echocardiography. Odibo et al25 found anatomy ultrasonography with selective fetal echocardiography to be more cost-effective than universal fetal echocardiography for diabetic patients. Additionally, fetal echocardiography has noneconomic costs. Rosenberg et al26 found that women referred for fetal echocardiography experienced increased anxiety.
Our study provides evidence that an unremarkable anatomic survey that includes outflow tracts can minimize the need for detailed fetal echocardiography. There were no cases of major CHD among 317 at-risk pregnancies after a normal anatomic survey. Based on a 95% probability, the maximum residual risk for major CHD is, at most, 9.4 per 1,000 pregnancies in our cohort, an incidence that is within the range reported for the general population.27 Therefore, an unremarkable anatomic survey can serve to reassure a high-risk patient that the risk of major CHD is similar to that of the general population. Moreover, whereas the size of our cohort only allows us to comment on a maximum residual risk of just less than 1%, future larger studies may be able demonstrate even lower residual risk, providing further justification for reserving fetal echocardiography for those with suspicious ultrasound findings, rather than a second screening.
Our findings expand on those of other investigators who have demonstrated limited clinical value to fetal echocardiography in more selected clinical populations. Both Bernard et al32 and Sekhavat et al34 found that fetal echocardiography did not detect additional major CHD after normal anatomy ultrasound scan in patients with diabetes. Starikov et al34 reviewed fetal echocardiography in patients with optimal cardiac imaging during anatomy scan and found no additional major CHD diagnosed. Our data support similar conclusions can be drawn for other risk factors for CHD.
Although New York University offers two anatomy ultrasound scans (one at 14–17 weeks of gestation and one at 20 weeks of gestation), we do not believe that women require two anatomy ultrasound scans to screen for major CHD successfully. The majority of patients in this cohort underwent one examination, and every case of major CHD (except one) was suspected based on a first examination. Similarly, whereas aortic and ductal arch views are included in our screening examination, they were the sole indication for fetal echocardiography in only one case of major CHD and contributed to the higher level of suspicion for CHD in a second patient. Therefore, our findings cannot be explained by this aspect of our screening protocol, and we believe other tertiary care centers may find similar results when analyzing their own experiences.
Our study has important limitations. First, the true gold standard for detecting major CHD would be universal neonatal echocardiography with close pediatric follow-up through childhood. This approach would yield the highest sensitivity for detecting major CHD. However, our study focuses on prenatal diagnosis of major CHD with the goal of appropriate patient counseling and management, including referral to a tertiary care center. Decisions on screening for major CHD need to be made by obstetric care providers before information received from a neonatal work-up, and our research question centers on the added benefit of using fetal echocardiography as a second screening test after a normal anatomy ultrasound scan in this context.
Secondly, although our ultrasound database does not include exhaustive clinical information (such as HbA1c levels or degree of relation for family history of major CHD) precluding a more detailed analysis of risk factors used by referring physicians, a major strength of the study is that the cohort of patients in the study reflects current referral patterns for fetal echocardiography and decisions made by providers. Similarly, because our cohort reflects actual referrals, a small minority of patients who were referred for echocardiography were not likely to be at increased risk for major CHD, such as those with echogenic intracardiac focus or seizure disorder not using antiepileptic medications. Finally, although it is possible that a patient with an unremarkable anatomy ultrasound scan at our institution received a diagnosis of major CHD at an outside institution, it is far more likely that a patient would be referred for fetal echocardiography secondary to concerning findings on anatomy scan. In fact, our review of neonatal intensive care unit records revealed a tetralogy of Fallot correctly diagnosed on anatomy ultrasound scan in a patient who underwent confirmatory echocardiography at an outside institution. Therefore, we believe limiting our cohort to fetal echoes at New York University allowed us to avoid potential confounding attributable to varying echocardiography protocols and would be unlikely to affect our conclusions.
Another important consideration in interpreting the results of this study is that ultrasound accuracy is highly dependent on operator experience. For centers with lower volume or less experience, fetal echocardiography may be of more value in detecting major CHD. Acherman et al14 do not include the level of experience of the various providers who performed the screening examinations in their study. Only 53% of major CHD cases that should be captured by four-chamber heart (atrioventricular septal defects and atrioventricular connection abnormalities) were diagnosed prenatally in their study. It is also possible that differences in patient compliance with prenatal care and sonography contributed to low detection rates.
In summary, our results indicate that in a single, high-volume, tertiary care institution, fetal echocardiography demonstrated limited utility in the detection of major CHD after a normal anatomy scan that includes outflow tract views. Although fetal echocardiography plays an important role in characterizing complex anomalies and in detecting minor CHD, our data question the utility of a screening fetal echocardiography based solely on risk factors. It may be reasonable to reserve referral for detailed fetal echocardiography for patients with abnormal or suboptimal cardiac views or with a significant extracardiac anomaly.
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© 2011 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.
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