Ultrasound Obstet Gynecol 2007; 29: 619–624 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/uog.4023
Population-based study of antenatal detection of congenital heart disease by ultrasound examination C. CHEW*, J. L. HALLIDAY†‡§, M. M. RILEY‡ and D. J. PENNY*§ *Department of Cardiology, Royal Children’s Hospital, Australia and New Zealand Children’s Heart Research Centre, †Public Health Genetics, Murdoch Childrens Research Institute and §Department of Paediatrics, University of Melbourne, Parkville and ‡Victorian Birth Defects Register, Department of Human Services, Victoria, Australia
K E Y W O R D S: antenatal diagnosis; congenital heart disease; prenatal screening; routine antenatal ultrasound
ABSTRACT Objectives Ultrasound-based screening is widely employed for the detection of congenital malformations in utero including congenital heart disease (CHD), but there is widespread variability in the efficacy of screening programs. We aimed to evaluate current antenatal detection rates of selected congenital heart defects in Victoria. Methods Data were collected from the Victorian Perinatal Data Collection Unit and Birth Defects Registry. There were 631 209 births in Victoria (1993–2002), of which 4897 cases had CHD. Cases included live births, stillbirths and termination of pregnancies because of CHD. We reviewed all cases from 1999 to 2002 with atrioventricular septal defect, simple coarctation of the aorta, double-inlet or -outlet ventricle, hypoplastic left heart syndrome, simple transposition of the great arteries (TGA), tetralogy of Fallot and truncus arteriosus. Outcome measures were antenatal diagnosis, pregnancy outcome and associated malformations. Results The overall birth prevalence of CHD from 1993 to 2002 in Victoria was 7.8/1000. The antenatal detection rate for the seven selected defects from 1999 to 2002 was 52.8%. All but 4.8% of the cases had an ultrasound examination at > 13 weeks’ gestation. Antenatal detection was highest for hypoplastic left heart syndrome (84.6%) and lowest for simple TGA (17.0%). Conclusions This study shows wide variation in the antenatal detection rate of CHD in Victoria. The low antenatal detection rate of TGA, a defect that should be detected easily, demonstrates suboptimal routine obstetric anomaly scanning. Copyright 2007 ISUOG. Published by John Wiley & Sons, Ltd.
INTRODUCTION Congenital heart disease (CHD) is an abnormality of the heart or great vessels that is present from birth.
Prevalence studies have estimated that CHD occurs in eight of every 1000 live births1 – 3 , with major congenital heart defects accounting for approximately half4 – 7 . This high prevalence makes it the most common birth defect, comprising approximately 27% of all birth defects in Victoria8 and 28% of all birth defects in Australia9 . CHD is, therefore, three times more common than identifiable chromosomal anomalies and four times more common than neural tube defects8,9 . Furthermore, it is the most life-threatening defect in the first month of life, accounting for approximately 20% of perinatal deaths10 – 12 . CHD is part of an identifiable syndrome or chromosomal defect in some patients, but in the majority it appears spontaneously with no identifiable risk factors. As a result, primary prevention is not possible, so the only means of changing the prevalence of CHD is by secondary prevention methods, which are based upon the early diagnosis of CHD. Antenatal diagnosis, through fetal echocardiography, facilitates implementation of secondary prevention methods in two ways. First, it enables parental counseling regarding the CHD diagnosis, prognosis, management and treatment, following which the pregnant woman may elect to terminate the pregnancy. Second, if the pregnancy is ongoing, antenatal diagnosis facilitates changes in obstetric and neonatal management which optimize outcome; for at least some lesions, antenatal diagnosis reduces mortality and morbidity13 – 18 . The mid-trimester or routine anomaly ultrasound scan assesses gestational age, fetal growth, placental location, maternal anatomy, amniotic fluid volume, plurality and fetal anatomy19,20 . The Royal Australian and New Zealand College of Obstetricians and Gynaecologists20 and the Australasian Society for Ultrasound in Medicine19 provide comprehensive guidelines on mid-trimester obstetric scanning, including a checklist of fetal anatomical structures that should be evaluated carefully to ensure detection of major anatomical abnormalities, including examination of the four-chambers and
Correspondence to: Assoc. Prof. J. L. Halliday, Public Health Genetics, Murdoch Childrens Research Institute, Royal Children’s Hospital, Parkville, Victoria, Australia (e-mail:
[email protected]) Accepted: 22 December 2006
Copyright 2007 ISUOG. Published by John Wiley & Sons, Ltd.
ORIGINAL PAPER
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ventricular outflow tracts of the fetal heart to detect CHD19,20 . Use of the mid-trimester routine anomaly ultrasound examination is highly variable. In some countries, such as Germany, France and Norway, there is a governmentsponsored policy of routine anatomical screening by ultrasound examination21 . In the UK and Australia, routine screening is accepted but not uniformly adopted or standardized21 . There have been many studies documenting obstetric ultrasound utilization in the UK and Europe2,7,22 – 25 , but Victorian data are limited to a study performed nearly 15 years ago. This study demonstrated that approximately 96.9% of pregnant women underwent obstetric ultrasonography, of whom 73.5% were between 16 and 20 weeks’ gestation26 . No other study has since evaluated utilization of routine anomaly ultrasound examination in Victoria. Routine population-based ultrasound screening for CHD is associated with specificities above 96%6,27 – 31 . However, despite this high specificity, there has been much debate about whether ultrasound screening is indeed efficacious and beneficial. Many retrospective and prospective studies on the sensitivity of both four-chamber and extended examinations of the fetal heart have been published, with a wide range of rates of detection of CHD. The variation in sensitivity is primarily due to differences between studies in the composition of the study population, the definition of CHD, the gestational age at which screening was performed, the level of training and experience of the ultrasonographers, and the length of postnatal follow-up for CHD case ascertainment. This population-based study aimed to determine the prevalence of CHD in Victoria and to evaluate the antenatal detection rate of seven selected congenital heart defects.
gestation have been collected on the birth form since 1999.
Birth Defects Register The Birth Defects Register (BDR) was established by the VPDCU for registration of birth defects diagnosed in children up to 15 years of age who were born in Victoria. The BDR collects information on all birth defects for live births, stillbirths and terminations of pregnancy (TOPs) (for a birth defect) occurring from 1 January 1982 in the State of Victoria. Data are collected from multiple sources, including the VPDCU birth form, hospital inpatient listings, perinatal death certificates, autopsy reports, cytogenetics reports, and maternal and child health nurses. This ensures high ascertainment of birth defects at different perinatal and childhood stages of life. Validation studies have been undertaken at regular intervals to assess the data quality and completeness of the BDR. The register classifies birth defects according to the British Paediatric Association (BPA) Classification of Diseases – Perinatal Supplement32 .
Database linkage In order to obtain obstetric histories for each of the cases, the BDR was linked to the VPDCU birth form using the maternal registration number. Additional data items obtained from the birth record were procedures and operations (ultrasound status), pregnancy outcome, type of labor and gestation.
Study populations
METHODS
Base population
Approval for the study was granted by both the Royal Children’s Hospital Ethics in Human Research Committee and the Victorian Department of Human Services Human Research Ethics Committee.
The base population consisted of all births (including live births, stillbirths and TOPs for birth defects) in Victoria between 1 January 1993 and 31 December 2002.
Data sources Victorian Perinatal Data Collection Unit The Victorian Perinatal Data Collection Unit (VPDCU) was established in 1982 under the Health Act of 1953 and operates under the aegis of the Consultative Council on Obstetric and Paediatric Mortality and Morbidity. The VPDCU is a population-based mandatory surveillance system that collects information on the health of mothers and babies using a standard birth form. The data are collected via the VPDCU birth form, which is completed by midwives for every birth in Victoria at and after 20 weeks’ gestation. Data on antenatal ultrasound examinations performed between 13 and 26 weeks’
Copyright 2007 ISUOG. Published by John Wiley & Sons, Ltd.
Total congenital heart disease population (for prevalence data) Cardiac anomalies reported between 1993 and 2002 were divided into three subsets of the BPA classification system32 : bulbus cordis anomalies and anomalies of cardiac septal closure (code 745), other congenital anomalies of the heart (code 746) and other congenital anomalies of the circulatory system (code 747). All cases in the BDR with one or more of the above codes were considered to have CHD and included in the prevalence calculations. Cases with an isolated defect associated with normal development were excluded. Codes excluded were 74700 (isolated patent ductus arteriosus), 74782 (isolated persistent fetal circulation) and 74550 (isolated patent foramen ovale).
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Antenatal detection of congenital heart disease Seven sentinel congenital heart defects (for antenatal detection data) A subset of the above CHD population, from 1999 to 2002, was selected for further data collection and analysis. Cases with at least one of the following defects were included: atrioventricular septal defect (AVSD; code 74562–74563), coarctation (CoA; code 74710–74719), double-inlet/outlet ventricle (code 74513, 74514, 74539), hypoplastic left heart syndrome (HLHS; code 74670–74679), transposition of the great arteries (TGA; code 74510–74512, 74516–74519), tetralogy of Fallot (TOF; code 74520–745290) and/or truncus arteriosus (TA; code 74500). The study was restricted to these defects for a number of reasons. First, the selected defects represent the spectrum of complex CHD reported by the International Clearinghouse for Birth Defects Monitoring33 , so comparative data are readily available. Second, they vary in their amenability to antenatal diagnosis (Table 1). Finally, any liveborn case with one or more of the above diagnoses would eventually present to the Royal Children’s Hospital (RCH) for cardiac surgery. This enabled linkage of records between the BDR and RCH to validate birth defect data for live births (see below). Furthermore, the study interval was restricted to the period when reporting of ultrasound examinations became routine at the BDR and VPDCU. From the data available, it was not possible to determine who performed the ultrasound examination, nor when or where it was performed. Therefore, the study was not evaluating specific operators, but examined outcomes of obstetric ultrasound scans carried out at between 13 and 26 weeks’ gestation, in a variety of settings, by operators with different training and experience.
Outcome measures The primary outcome of the study was whether or not an antenatal diagnosis had been made by ultrasonography. Secondary outcome measures included ultrasound utilization from 2000 to 2002 (no ultrasound examination, single scan or multiple scans) and chromosomal associations. Depending on pregnancy outcome (TOP, stillbirth, neonatal death or survived for more than 28 days), four different methods were employed to determine, for each case, whether an antenatal diagnosis of CHD was made. VPDCU and BDR files were reviewed for each stillbirth. Data sources included the VPDCU birth form, cytogenetics reports and autopsy reports. RCH records of patients who were liveborn and survived more than 28 days were reviewed and compared with linked data in the BDR. Cases classified as neonatal death (died within 28 days) were divided into two groups. The first consisted of cases that died at an obstetric hospital and were examined in the same way as for stillbirths. The second group comprised cases that were transferred to the RCH and died subsequently. These were examined
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as described for live births. An antenatal diagnosis of CHD was assumed for the TOP population, because the BDR only collects data on TOP for a birth defect, not psychosocial reasons. All CHD cases were reviewed individually by a pediatric cardiologist experienced in fetal cardiac ultrasonography (D.J.P.) with respect to likelihood of antenatal diagnosis using four-chamber and ventricular outflow tract views. This reviewer was blinded to the antenatal findings above. On the basis of the experience of this expert cardiologist, and on findings from comparable institutionbased studies34 – 36 , each case was classified as: potentially detectable on four-chamber view, potentially detectable on four-chamber and ventricular outflow tract view or not readily detectable on four-chamber or ventricular outflow tract view (Table 1).
Data analysis All data were collected and recorded in a Microsoft Access (Redmond, WA, USA) database and exported to Stata version 8 (StataCorp, College Station, TX, USA) for statistical analysis. Binomial exact 95% CI are stated where appropriate and proportions were compared using a two-tailed binomial probability test for binomial random variables. Poisson regression was used to estimate the average trend in the birth and live birth prevalence of CHD. Categorical data were compared using Pearson Chi-square analysis.
Table 1 Cardiac anomalies detectable in four-chamber view (4CV) and ventricular outflow tract (VOT) view Anomalies potentially detectable on 4CV alone Atrial isomerism Atrioventricular septal defect Critical pulmonary stenosis/atresia Dextrocardia Double-inlet left ventricle Double-outlet right ventricle Ebstein’s anomaly Hypoplastic left heart syndrome Interrupted aortic arch and large VSD Large VSD Mitral atresia Taussig–Bing anomaly Tetralogy of Fallot Tricuspid atresia Anomalies potentially detectable on 4CV and VOT view Aortic stenosis Simple transposition of the great arteries Subaortic stenosis Truncus arteriosus Anomalies not readily detectable on 4CV or VOT view Anomalous left coronary artery from the pulmonary artery Aortopulmonary window (aortopulmonary septal defect) Double aortic arch Pulmonary artery sling Simple coarctation Total anomalous pulmonary venous drainage VSD, ventricular septal defect.
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RESULTS
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Between 1 January 1993 and 31 December 2002, there were 631 209 births in Victoria, of which 626 781 were live births. During this period, 4897 births were diagnosed with CHD, of which 4295 were live births. The overall birth prevalence, including live births, TOPs and stillbirths, of CHD in Victoria was 7.8 (range for annual prevalence, 6.9–10.0) per 1000 from 1993 to 2002. The rate of CHD births had increased by 2.4% (95% CI, 1.4–3.4%; P < 0.001) per year over the period. The live birth prevalence of CHD in Victoria from 1993 to 2002 was 6.9 (range for annual prevalence, 5.9–9.0) per 1000. The rate of CHD live births had increased by 2.5% (95% CI, 1.5–3.6%; P < 0.001) per year over the period. Data from 2000–2002 showed that 95.8% of all women had at least one ultrasound examination in pregnancy and, specifically, that 95.2% of women carrying a fetus with CHD had an ultrasound performed at > 13 weeks’ gestation.
Antenatal detection rates There were 451 cases with one of the seven sentinel cardiac defects (Table 2), of which 238 (52.8%; 95% CI, 48.0–57.5) had an antenatal diagnosis over the study period. Of the 451 cases, 331 (73.4%) were potentially detectable on four-chamber view alone. If the ventricular outflow tract view was added to the four-chamber view, a further 74 cases were potentially detectable. Thus, under ideal circumstances, routine anomaly ultrasound examination would have been expected to detect 405 (89.8%) of the 451 cases. Antenatal detection rates varied considerably between the seven sentinel defects (Table 2 and Figure 1). The highest antenatal detection rate was associated with HLHS (84.6%; 95% CI, 74.7–91.8) and the lowest with simple TGA (17.0%; 95% CI, 7.6–30.8). There were 187 698 births and 1647 CHD births from 2000 to 2002, but 2404 births (1.3%) and 110 CHD births (6.7%) were excluded as use of ultrasound was recorded as ‘unknown’. In the final population, 97.8% of all births and 97.6% of CHD births had an ultrasound Table 2 Antenatal detection rates for the seven sentinel defects (1999–2002)
Defect Hypoplastic left heart syndrome Double-inlet/outlet ventricle Truncus arteriosus Atrioventricular septal defect Tetralogy of Fallot Simple coarctation Simple transposition of the great arteries Total
n
Number diagnosed antenatally (%; 95% CI)
78 73 27 71 109 46 47
66 (84.6; 74.7–91.8) 54 (74.0; 62.4–83.5) 18 (66.7; 46.0–83.5) 33 (46.5; 34.5–58.7) 47 (43.1; 33.7–53.0) 12 (26.1; 14.3–41.1) 8 (17.0; 7.6–30.8)
451
238 (52.8; 48.0–57.5)
Copyright 2007 ISUOG. Published by John Wiley & Sons, Ltd.
Antenatal diagnosis (%)
Prevalence data 80 *
* 60 *
*
TGA
CoA
40
20
0
HLHS DIV/ DOV
TA
AVSD TOF
Congenital heart disease
Figure 1 Comparison of antenatal detection rates for the seven sentinel defects in our study (1999–2002) (), in Europe (1996–1998)25 ( ) and in Paris (1995–2000)37 ( ). *P < 0.001. AVSD, atrioventricular septal defect; CoA, aortic coarctation; DIV/DOV, double-inlet/outlet ventricle; HLHS, hypoplastic left heart syndrome; TA, truncus arteriosus; TGA, transposition of the great arteries; TOF, tetralogy of Fallot.
examination during pregnancy. The routine anomaly ultrasound scan, between 13–26 weeks’ gestation, was performed for 93.6% of all births and 93.0% of CHD births. Of the 451 cases, 76 were associated with identifiable chromosomal defects and 42 (55.3%; 95% CI, 43.4–66.7) had an antenatal diagnosis.
DISCUSSION Our study investigated the antenatal detection rate of selected congenital heart defects in Victoria between 13 and 26 weeks’ gestation, by ultrasound operators with variable training and expertise and in settings including private obstetric practices, hospital antenatal clinics and specialist ultrasound centers. Prevalence studies and analysis of ultrasound utilization were performed on data obtained from the VPDCU, for study periods of 10 years and 3 years respectively. Furthermore, seven sentinel congenital heart defects were selected for detailed examination. Records of all infants born in Victoria between 1 January 1999 and 31 December 2002 with one or more of the seven sentinel CHD defects were reviewed. Our study produced four main findings. First, the prevalence of CHD in Victoria (7.8/1000) is consistent with that of previous reports1 – 3 . Second, observed overall antenatal detection rates (52.8%) were significantly lower than expected antenatal detection rates for the seven sentinel defects (89.8%). Third, there was wide heterogeneity in the rates of antenatal diagnosis, with best antenatal detection associated with an abnormal four-chamber view. Finally, routine anomaly ultrasound examination was performed in 93.6% of all births and 93.0% of CHD births. Two population-based studies, in which ultrasound examination was performed in many centers in a geographically defined low-risk population, have
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Antenatal detection of congenital heart disease documented similar rates of antenatal detection of CHD25,37 . In comparing our detection rates with those of these studies, it is clear that for some lesions seen with a four-chamber view our antenatal detection rate is comparable; however, for others, including TOF, CoA and TGA, it is not as high (Figure 1). Given the rapid advances in routine anomaly screening over the past 20 years, the low antenatal detection rate of selected congenital heart defects in Victoria may benefit from careful review to determine where improvements need to be made. The reasons for the lower antenatal detection rates are not known, but may reflect major differences in operator experience and availability of sophisticated ultrasound equipment across the State. This study highlights the overall need for cardiac training at regular education sessions run by professional organizations to enhance operator skill development in this complex area. Of particular concern is the low antenatal detection rate of TGA because antenatal diagnosis of this lesion has repeatedly demonstrated improvement in outcome15,16,38 . A reduction in both perinatal mortality and morbidity in these infants results from in-utero transport to a specialist center, where there is early use of prostaglandins and availability of interventional procedures. In addition to low antenatal detection rates overall, 55.3% of chromosomally abnormal CHD cases were not diagnosed antenatally. This means that the choice to interrupt the pregnancy or the time afforded to understand the diagnosis and prognosis and plan appropriate perinatal management is not provided to such parents. The present study included an analysis of antenatal detection rates for only seven important congenital heart lesions. The results were not therefore indicative of the overall antenatal detection rate of CHD in Victoria. The examination included these defects specifically because of the availability of patient data, as it was known that all liveborn infants with one of these defects would inevitably present to RCH for cardiac surgery. This contrasts with the remainder of the CHD population in which there is wide variability in primary care institute and postnatal management. Investigation of the statewide antenatal detection rate of CHD would require a large multicenter study. In conclusion, despite the knowledge that antenatal diagnosis of CHD improves outcomes for affected children, and that there is widespread antenatal ultrasonographic screening for birth defects in Victoria, almost half of the infants with severe CHD do not have an antenatal diagnosis. This problem is particularly evident for defects that can be detected on the outflow tract view. Specialist skills in this area should be included in professional development sessions for those performing antenatal ultrasonography.
ACKNOWLEDGMENTS Many thanks to Susan Donath of the Clinical Epidemiology and Biostatistics Unit, Murdoch Childrens Research Institute, for assistance with the statistical analysis.
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