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Antenatal diagnosis of fetal heart malformation

The incidence of fetal cardiac malformation amongst live births (eight per 1000) is six times greater than chromosomal abnormalities and four times that of neural tube defects.

Dr Simon MeagherFRANZCOG

at 11 to 14 weeks gestation

Furthermore, over half of these babies have a significant defect which contributes to 20 per cent of all neonatal deaths and up to 50 per cent of infant deaths.1 Importantly, there is good evidence that prenatal detection of these major defects improves postnatal outcome, particularly for lesions such as transposition of the great arteries (TGA) and other arterial duct dependent lesions. For this reason amongst others, there

is increasing international interest in the prenatal detection of congenital heart defects (CHD).

Detection rates of fetal cardiac malformation in the mid-trimester is variable and dependent on many factors, including operator expertise, patient size, fetal position and the complexity of the specific cardiac lesion. For example, a recent population study in Victoria revealed a detection rate for the more obvious abnormalities such as hypoplastic left heart and double outlet/inlet ventricle of 84 per cent and 74 per cent respectively, whereas detection rates for more subtle lesions such as coarctation and transposition were 26 per cent and 17 per cent respectively.2 Identification of all these abnormalities in the first trimester is unquestionably more difficult. The fetus at 11 to 14 weeks is approximately 6 to 8 cm in length. The fetal heart size at 12 weeks measures 11 mm long and 6 mm across, therefore, similar in size to the fifth fingernail. This said, the axial and lateral resolution of current ultrasound systems using high frequency endovaginal ultrasound is 0.1 mm. Also, recently published detection rates in specialist centres now approximate the detection rates at the mid-trimester and thus it is a matter of time before the majority of CHD in Australia will become detectable at 11 to 14 weeks.

Nuchal translucency and heart defects

In the first trimester, an increased nuchal translucency (NT) is a strong indicator of underlying congenital heart disease, far stronger than a past history of CHD or diabetes. Of all births with CHD, 25 to 30 per cent would be expected to demonstrate an increased NT at 11 to 14 weeks. Conversely, the incidence of CHD in fetuses with an increased NT is five per cent. The greater the NT, the greater the chance of underlying CHD ( Table 1). Therefore, patients with an NT of greater than 8.5 mm and normal chromosomes over 60 per cent will have underlying CHD.3 Thus, in patients with a normal karyotype following chorionic villus sampling or amniocentesis, the increased NT should be regarded as a pointer to cardiac malformation. Indeed, once the NT reaches 3 mm, a targeted fetal echocardiogram should be considered. Of note in the presence of

an increased NT, there is no obvious bias towards any particular lesion or sidedness of heart defect.

Table 1.Bands of risk for increased nuchal translucency and congenital heart malformation.3

NT Range Incidence of major CHD

NT in the range 2.5-2.9 mm 2.4% (10/416)

NT in the range 3.0-3.4 mm 2.6% (8/306)

NT in the range 3.5-4.4 mm 3.1% (12/384)

NT in the range 4.5-6.4 mm 8.3% (13/157)

NT in the range 6.5-8.4 mm 19% (8/42)

NT in the range > 8.5 mm 64.3% (9/14)

Tricuspid regurgitation

Tricuspid regurgitation (TR) at 11 to 14 weeks is seen in up to 70 per cent of fetuses with Trisomy 21 and has been introduced in the united kingdom to the Fetal Medicine Foundation first trimester nuchal translucency program. Like nuchal translucency, TR is also an indicator of CHD and recent evidence suggests its association with CHD may be independent of nuchal thickening (Figures 3a and 3b). Its assessment in the first trimester may help subselect the group of fetuses with an increased NT and congenital heart malformation. While TR assessment is not yet routine practice in Australia, it seems likely that assessment of this marker in the future may help identify fetuses with major CHD.

Ductus venosus

Absence or reversal of flow in the ductus venosus (DV) at 11 to 14 weeks is an indicator of Down syndrome. Recent data, however, also show that Doppler velocimetry of the DV can help improve the predictive capacity of increased NT in the detection of major congenital heart defects in chromosomally normal fetuses. In patients with a thickened NT and normal chromosomes following invasive testing, the finding of an absent or reversed A-wave in the ductus venosus is associated with a three-fold increase in the likelihood of a major cardiac defect, whereas the finding of normal ductal flow is associated with a halving in risk of such defects.5

Therefore, in patients with normal karyotype following invasive testing where absent ductus venosus (ADV) or reversed ductus venosus (RDV) has been observed, a fetal echocardiogram should be considered. There is also data emerging to suggest that an abnormal first trimester DV blood flow is a risk factor not only for CHD, but an indicator of other structural anomalies and perinatal death in fetuses with normal NT.4

Text continued on page 38.

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Figure 1. A normal four-chamber view of the heart at 12 weeks on both B-mode (left) and colour Doppler examination (right). Normal atrial and ventricular symmetry is observed.

Figure 2. Normal outflow tracts at 12 weeks are demonstrated on this duplex image in which B-mode is shown on the left and directional power Doppler on the right. The calibre and direction of the main pulmonary artery (MPA), right pulmonary artery (RPA), aorta (AO), ductus arteriosus (AD) and descending aorta (DA) are all seen more easily with colour Doppler examination.

Figures 3a and 3b. Doppler assessment of the right heart reveals tricuspid regurgitation which indicates the possibility of underlying CHD.RV = right ventricle LA = left atrium

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Assessment of fetal heart anatomy

The fetal heart is best assessed by both transabdominal and transvaginal examination. There should be few reasons why a transvaginal examination is not offered routinely to all patients at the 11 to 14-week scan. Accepting the limitations of probe movement and accepting the unpredictability of fetal position, greater cardiac detail is obtained in most patients with this approach (Figure 1). The ease of recognition of normal fetal heart anatomy at 12 versus 11 weeks is striking. A one-week increase in fetal size makes a significant difference in cardiac anatomy resolution. For this reason, patients are best booked after 12 weeks of gestation. The identification of normal cardiac structures at 12 weeks has a strong negative predictive value which is of clinical relevance in the setting where first trimester risk factors have been identified (see below). The four chamber view of heart and outflow tracts are identifiable in skilled hands in up to 90 per cent of patients at 12 weeks.

Colour Doppler examination in the first trimester is a powerful tool in the routine assessment of fetal cardiac structure and will provide detail of the outflow tracts in patients where views on gray scale are limited (Figure 2). Colour Doppler examination has the potential to unveil TR or muscular septal defects, which for the greater part are not seen on B-mode examination at this stage in gestation (Figure 3). 4D ultrasound using spatio-temporal image correlation (STIC) technology is emerging as a useful screening and diagnostic tool for CHD at the mid-trimester and beyond. At this point in time however, its application in the first trimester is limited. However, 3D static volume acquisition of the heart using colour (‘glass body’ render) has potential in its assessment of cardiac function including tricuspid regurgitation and septal defects. With respect to fetal cardiac malformation, the image sequences upon which mid-trimester diagnoses rely are similar in the first trimester. In transposition of the great vessels, the major arteries arise from the heart in parallel (Figure 6 ); in Tetralogy of Fallot the aorta overrides the inter- ventricular septum (Figure 7); and in hypoplastic left heart, the left ventricle is small and the right heart chambers and right ventricular outflow tract are dilated (Figures 5a and 5b). The diagnoses of more subtle abnormalities such as right-sided aortic arch and atrioventricular (AV) canal defects can be more difficult (Figure 8a and Figure 9).

Conclusion

Improved high frequency vaginal probes, increasing sensitivity of colour Doppler technology and ever increasing maternal body habitus, should steer clinicians towards routine endovaginal ultrasound examination of the fetal heart during the first trimester. Patient acceptance of a vaginal scan is predictably high once the benefits of the examination are explained. While the learning curve in first trimester fetal heart diagnosis may be steep, current evidence suggests that a diagnosis may be reached in over 90 per cent of cases at 11 to 14 weeks gestation.

The first trimester provides a unique opportunity in that there are several markers at this time which lead to the diagnosis of CHD. One in every three cases of major CHD present with an increased NT and abnormal Doppler velocimetry of the ductus venosus. Also, Doppler assessment of the tricuspid valve can help improve the predictive capacity of increased NT in the detection of major congenital heart defects in both euploid and aneuploid fetuses.

While first trimester detection rates of CHD in specialist centres are now approaching second trimester detection rates, it may take time before this translates into routine practice in low-risk populations. While climbing this learning curve, caution needs to be exercised in

the first instance, with a low threshold for seeking a second opinion, or at least considering a repeat examination of the fetal heart later in pregnancy.

While the resolution of ultrasound increases and the understanding of cardiac diagnosis improves, it seems unlikely however, that the 11 to 14-week scan will completely replace the mid-trimester cardiac assessment in the near future. This is not to say we should not strive to reach a diagnosis at earlier stages in pregnancy, particularly since there is a captive population who are having a routine first trimester scan performed for other reasons, namely NT assessment.

References

1. Yagel S, Cohen SM and Achiron R. Examination of the fetal heart by five short-axis views: a proposed screening method for comprehensive cardiac evaluation. ultrasound Obstet Gynecol 2001; 17:367-369.2. Chew C, Halliday JL, Riley MM and Penny DJ. Population-based study of antenatal detection of congenital heart disease by ultrasound examination. ultrasound Obstet Gynecol 2007; 29:619-624.3. Ghi T, Huggon IC, Zosmer N and Nicolaides kH. Incidence of major structural cardiac defects associated with increased nuchal translucency but normal karyotype. ultrasound Obstet Gynecol 2002; 18:610-614.4. Oh C, Harman C, Baschat AA. Abnormal first-trimester ductus venosus blood flow: a risk factor for adverse outcome in fetuses with normal nuchal translucency. ultrasound Obstet Gynecol 2007; 30:192-196.5. Maiz N, Plasencia W, Dagkils T, Faros E, Nicolaides k. Ductus venosus Doppler in fetuses with cardiac defects and increased nuchal translucency thickness. ultrasound Obstet Gynecol. 2008 March; 31(3): 256-60.

FIRST INTERNATIONAL ASIA PACIFIC MEETING ON POLYCYSTIC OVARY SYNDROME

Jointly organised by Department of Obstetrics and GynaecologyThe University of Hong Kong

andThe Androgen Excess PCOS Society

17–18th JANUARY 2009Venue: Cheung Kung Hai Conference Centre

The University of Hong Kong, Hong Kong

Polycystic ovary syndrome is the commonest endocrine disorder in women of reproductive age. There is substantial heterogeneity of symptoms and signs among women from different ethnic origins, which may have an impact on the treatment and the long term prognosis of this syndrome. This meeting aims to highlight the special features of the syndrome encountered in the Asia Pacific region, features Asian, Australian and international faculties.

Registration Fee US$320Further information: Prof Robert Norman email: robert.norman@adelaide.edu.au

Conference secretariat – Veronica Cheng or Rachel Lee, c/o PC Tours and Travel

email: veronica@pctourshk.comwebsite www.hku.hk/obsgyn

Illustrations continued on pages 39 to 41.

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Vol 10 No 3 Spring 2008 39

Figures 4a and 4b. These figures demonstrate normal and reversed ductus venosus waveform at 12 weeks gestation. The presence of a reverse A-wave raises the possibility of CHD.

Figure 5a. Hypoplastic left heart at 12 weeks. On the four-chamber view, a dilated right atrium (RA) and dilated right ventricle (RV) are seen. The left atrium is small and the left ventricle hypoplastic.

Figure 5b. Hypoplastic left heart at 12 weeks. The right ventricular outflow tract view demonstrates a dilated main pulmonary artery (MPA) and dilated right pulmonary artery (RPA). Ductus arteriosus (DA).

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Figure 6. Transposition of the great vessels at 12 weeks. Both the aorta (AO) and pulmonary artery (PA) arise from the heart in parallel.

Figure 7. Tetralogy of Fallot at 12 weeks. The dilated aorta is seen sitting astride the interventricular septum.

Figure 8a. Right-sided aortic arch at 12 weeks. The three-vessel tracheal view reveals the transverse aortic arch (TAo) diverging from the main pulmonary artery (PA) and to the right of the trachea.

Figure 8b. 3D ultrasound demonstrates cardiac exstrophy at eight weeks.

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Vol 10 No 3 Spring 2008 41

Figure 9. Atrioventricular (AV) canal defect at 12 weeks. There is a common AV valve, absent septum primum and ventricular septal defect.

Figure 10. Hypoplastic right heart at 12 weeks. RV=right ventricle, LV=left ventricle, PE=pericardial effusion.

Ob/GynUltrasound

Workshop (Part 1)

Date: 6th–7th December 2008

Final Notice– Book this date

GE Healthcare

in association with Dr. Simon MeagherDirector, Monash Ultrasound for Women

Melbourne: Venue be confirmed

The 2008 program presents PART 1 of a two-part interactive lecture series in Ob/Gyn ultrasound and is directed at Sonographers, Radiologists, General Obstetricians and COGU trainees. The lecture series wil be conducted over two days and will present over 1500 video clips of fetal and gynaecological pathology

For program details, visit our website www.ultrasound.com.au

Registration numbers are limited. Book now to avoid disappointment

For more information please emailultrasound@ultrasound.com.au