This chapter should be cited as follows:
DeVore GR, Glob. libr. women's med.,
ISSN: 1756-2228; DOI 10.3843/GLOWM.419123

The Continuous Textbook of Women’s Medicine Series – Obstetrics Module

Volume 18

Ultrasound in obstetrics

Volume Editors: Professor Caterina M (Katia) Bilardo, Amsterdam UMC, Amsterdam and University of Groningen, Groningen, The Netherlands
Dr Valentina Tsibizova, PREIS International School, Florence, Italy

Chapter

Second- and Third-Trimester Screening for Congenital Heart Defects: A Practical Approach

First published: October 2024

Study Assessment Option

By completing 4 multiple-choice questions (randomly selected) after studying this chapter readers can qualify for Continuing Professional Development awards from FIGO plus a Study Completion Certificate from GLOWM
See end of chapter for details

INTRODUCTION

Congenital heart disease (CHD) is the most common malformation (10/1000 to 16.5/1000),¹ with a risk surpassing that of trisomy 21 (1.6/1000)² and neural tube defects (0.71 to 0.94/1000).³ However, for the past 40 years, the emphasis on prenatal detection has been on detecting trisomies 21, 13 and 18 as well as neural tube defects using various combinations of ultrasound and blood tests to screen for these malformations. During the evolution of aneuploidy screening, the detection of CHD evolved, but at a slower pace. For example, the first reports that abnormalities of the four-chamber view (4CV) were associated with a number of congenital heart defects appeared in 1985⁴ and 1987.⁵ Following the observation that alterations in the size and shape of the ventricles and/or atria in the 4CV identified fetuses at risk for CHD, a study in 1992 reported how to image the outflow tracts during a screening examination of the fetal heart.⁶ After more than 30 years, the screening examination of the fetal heart is now the standard of care when performing a second- or third-trimester ultrasound examination of the fetal heart.^6,7 While first-trimester screening for CHD has been suggested by some investigators, screening during this time of pregnancy has not been universally implemented.^8,9 Therefore, the purpose of this chapter is to provide a practical approach for optimal screening of the fetal heart during the second and third trimesters of pregnancy.

SCREENING GUIDELINES

The most recent screening guidelines from the International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) for evaluating the fetal heart recommend a transverse sweep through the upper abdomen and chest, which identifies the fetal stomach, 4CV, left ventricular outflow tract (LVOT), right ventricular outflow tract (RVOT), and the three-vessel-and-trachea view (3VTV) (Figure 1, Video 1).¹⁰

DETERMINATION OF SITUS

Video 2 illustrates the following steps to identify fetal situs.

• Place the patient so that structures on the examiner’s right are seen on the right side of the screen and those on the examiner’s left are on the left side of the screen.
• Next, lift the edge of the right side of the transducer off the maternal abdomen to see if the corresponding shadow is on the right side of the screen. If it is not, rotate the transducer 180° or flip the image on the screen using the relevant key on the machine.
• Once this is done, identify the fetal head to determine if the fetus is vertex, transverse or breech.
• Then, sweep the transducer beam through the fetal trunk to identify the position of the stomach and 4CV to ascertain that they are on the left side of the fetal body.

ORIENTATION OF THE FOUR-CHAMBER VIEW WITHIN THE FETAL CHEST

Once situs has been determined, the next step is to identify the position of the fetal heart within the chest. The angle should be 45° (range 25–65°).¹¹ Cardiac malformations have been associated with both right and left axis deviation of the 4CV.^11,12 Video 3 illustrates how this is accomplished using the following steps.

• Freeze the 4CV image on the screen and do the following:
  • Identify the edge of the ribs on the right and left sides of the chest and draw a line connecting the ends of the ribs (Figure 2A).The length of the line is divided by two to determine the mid-position.
  • Draw a second line to the mid-point of the first line (Figure 2B).
  • Draw a line from the spine to the end of the second line. This identifies the mid-point of the chest (Figure 2C).
  • Using the angle tool, draw a fourth line along the interventricular septum. This computes the angle between the septum and the midline drawn through the chest (Figure 2D).
• Another approach is to use an automated method available on several of the commercially available systems that automatically measure the axis and provide a color code of the normal axis (green), outside of which would be considered abnormal (red) (Figure 3).

MEASUREMENT OF THE SIZE OF THE FOUR-CHAMBER VIEW

The cardiothoracic ratio is a surrogate for assessing the size of the fetal heart. In 2021, Sompagdee et al. provided normal reference interval values (5th, 10th, 50th, 90th, 95th) for the cardiothoracic ratio measured with diameters (Video 4), area and circumference using gestational age and the biparietal diameter as independent variables (Figure 4).¹³ In the ISUOG fetal cardiac screening guidelines, the size of the 4CV is only inferred in a table which states that the heart should occupy one-third of thoracic area.¹⁰ ISUOG’s guideline on the performance of third-trimester obstetric scan states that the normal cardiothoracic circumference ratio in the third trimester is approximately 0.45 and should be no greater than 0.5 (Figure 5).^10,14 ,^{15 16}Neither guideline provides a reference for quantifying the 5th or 95th percentiles when measuring the cardiothoracic ratio nor is it acknowledged that the cardiothoracic ratio assumes that the chest is of normal size. In practice, it is preferable to measure directly the end-diastolic size of the 4CV and not assume its size is increased or decreased based upon its ratio to the size of the chest. Evaluation of the size of the 4CV can be accomplished using one of several measuring tools available on most ultrasound machines and correlating the size of the heart with biometric measurements such as the biparietal diameter, head circumference, abdominal circumference, femur length or estimated fetal weight, as well as gestational age.

The tools for measuring the area and circumference are as follows: (1) two-diameter method in which the longest length. and widest width of the four-chamber view are measured (Figure 6A),¹⁷ (2) the point-to-point method, which requires a manual trace (Figure 6B), and (3) the ellipse method, which uses electronic calipers (Figure 6C).¹⁸ Recent publications have provided calculators to compute the z-score of the end-diastolic size of the 4CV,^17,18 and Supplement 1 – Heart Size provides a calculator that computes the size of the 4CV using the three methods listed in Figure 6 using the estimated fetal weight as the independent variable.

		Clear Cells
	Enter Measurements in the Yellow Cells
	EFW (grams)
	END-DIASTOLIC MEASUREMENTS		Z-Score	Z-Score Percentile			Mean	Sd
	WIDTH (mm)
	LENGTH (mm)
	END-DIASTOLIC AREA (mm2)		Z-Score	Z-Score Percentile			Mean	Sd
	Point-to-Point Trace
	Ellipse
	Length and  Width
	END-DIASTOLIC CIRCUMFERENCE (mm)		Z-Score	Z-Score Percentile			Mean	Sd
	Point-to-Point Trace
	Ellipse
	Length and  Width

1

Heart size calculator.

GESTATIONAL AGE AFFECTS IMAGE QUALITY

Figure 7 and Video 5 illustrate 4CV clips at gestational ages of 16, 20, 24, 28, 32, 34 and 36 weeks, demonstrating how the clarity of the structures of the 4CV improves with gestational age. While the screening examination is usually performed between 18 and 22 weeks, a later gestational age may be required in obese patients.¹⁹

ANATOMY OF THE LEFT VENTRICLE

The left ventricle (LV) lies within the left side of chest, beneath the right ventricle (RV). It is shaped like a bullet (Figure 8A, Video 6), with a clearly defined apex. If the end-diastolic image of the 4CV contains the inferior papillary muscle, the plane of the 4CV would not be accurately imaged (Figure 8B). The septal leaflet of the mitral valve inserts higher on the interventricular septum than does the tricuspid valve (Figure 8C).The mid-portion of the LV should demonstrate movement of the interventricular septum towards the center of the chamber. Figure 9 illustrates movement of the ventricular and septal walls using speckle tracking. In the normal fetus the left side of the ventricular septum moves inwards towards the chamber, while the right side of the septum has no or little movement (Figure 9, Video 7). Visual inspection of the lateral wall thickness of the LV should be similar to that of the RV.

ANATOMY OF THE RIGHT VENTRICLE

The right ventricle is more globular in shape, with the apex being “blunted” (Figure 10A, Video 6). A band can also be observed running from the apex to the valve insertion, located in the center of the chamber (Figure 10B). During ventricular systole, the interventricular septum does not move towards the center of the RV as it does to the center of the LV (Figure 9, Video 7). The tricuspid valve inserts on the septal wall lower than the mitral valve and is opposite the “bend” of the septum at this level, as illustrated by the yellow line in Figure 10B. The moderator band, which is located between the septal and lateral apical walls of the RV, often obliterates the apex in systole (Figure 10C, Video 6). Visual inspection of the lateral wall thickness of the RV should be similar to that of the LV.

ANATOMY OF THE INTERVENTRICULAR SEPTUM

The interventricular septum is triangular, with the apex forming at the insertion of the tricuspid and mitral valves into the septum. As mentioned above, the septal wall of the LV moves towards the center of the chamber while the septal wall of the RV has minimal or no movement towards the center of the RV chamber (Video 7). Since the ventricular septum is triangular, measurement of its width is fraught with error, since it tapers from the base to the apex of the septum. Recently, a study was published in which the septal area was measured at both end-diastole and end-systole and found no difference between the two areas (Figure 11).²⁰ A calculator is provided that computes the z-score of the septal thickness (Supplement 2 – Septal Calculator).²⁰

			Clear Cells
	Enter Measurements in the Yellow Cells
	Gestational Age (Weeks)	BPD (cm)	HC (cm)	AC (cm)	FL (cm)	EFW (grams)
		End-Diastolic Area (cm2)	End-Systolic Area (cm2)	End-Diastolic Mid-Chamber Width (mm)	End-Diastolic Length (mm)		End-Diastolic Width/Length Ratio for the Mid-Chamber Width
							Z-Score	Centile
	GA Z-Score
	GA Centile
	BPD Z-Score
	BPD Centile
	HC Z-Score
	HC Centile
	AC Z-Score
	AC Centile
	FL Z-Score
	FL Centile
	EFW Z-Score
	EFW Centile

2

Septal calculator.

ANATOMY OF THE LEFT ATRIUM

Of the atrial chambers, the left atrium (LA) is the most important for identifying CHDs. The LA is shaped like a sausage and has three important anatomical features that should be identified during the screening examination (Figure 12, Video 6). The first is identification of two pulmonary veins entering the LA (Figure 12A). One vein enters near the atrial septum and the second vein enters near the back lateral wall of the atrial chamber. The second is identification of the integrity of the interventricular septum with the atrial septum to exclude an ostium primum defect (Figure 12B). The third is identification of the foramen ovale in which blood flows from the right atrium (RA) to the LA (Figure 12C) as demonstrated by the foramen ovale within the left atrial chamber during the cardiac cycle (Figure 12C).

ANATOMY OF THE RIGHT ATRIUM

The right atrial chamber is globular in shape (Figure 12, Video 6). In the 4CV there are no major anatomical landmarks except occasionally a flap of the Eustachian valve can be observed near the back wall of the atrial septum. In a study of the size, shape and contractility of the atrial chambers, it was reported that, although the atrial chambers are of different shapes, their end-diastolic areas were similar (Figure 13).

IDENTIFICATION OF THE OUTFLOW TRACTS

To exclude structural malformations of the aorta and pulmonary artery, there are three principles that should be considered. (1) As the aorta and main pulmonary artery immediately exit their respective ventricles, they should be perpendicular to one another; (2) the main pulmonary artery should demonstrate bifurcation into the right and the left pulmonary arteries and (3) the aorta should demonstrate continuity between the ascending aorta, the aortic arch and descending aorta. Using the current screening protocol illustrated in the ISUOG guidelines,¹⁰ only two of the three criteria are met.

Criterion 1. The perpendicular relationship of the ascending aorta and main pulmonary is identified from the three-vessel view in which the long axis of the main pulmonary artery is perpendicular to the short axis of the aorta (Figure 1D, Video 1).¹⁰

Criterion 2. The branching of the right and left pulmonary arteries exiting the main pulmonary artery is identified in the RVOT three-vessel view (Figure 1D, Video 1).

Criterion 3. Although a portion of the transverse aortic arch is visualized at the level of the tracheal view, the aortic arch is not completely visualized nor the descending aorta, therefore precluding the exclusion of an interrupted aortic arch (Figure 1C,E, Video 1).

To resolve the imaging deficiency listed under Criterion 3, there are two approaches using two of the four screening views of the heart proposed in the ISUOG screening guidelines as the reference point for rotation of the transducer to identify the continuity between the ascending aorta, aortic arch and the descending aorta.

Option 1. Identification of the continuity between ascending aorta, aortic rch and descending aorta using the left outflow tract view as the reference point for rotation of the transducer

In 1992, I described a technique to image the continuity between the ascending aorta, the aortic arch and the descending aorta, as well as demonstrated the ascending aorta and main pulmonary arteries to be perpendicular to each other as they exit their respective ventricles.⁶ The description of this technique was incomplete in the ISUOG guidelines. Therefore, I would like to suggest the following approach.

In the study described in 1992,⁶ the 4CV was imaged with the interventricular septum perpendicular to the ultrasound beam (Figure 14A). After imaging the 4CV, the transducer beam is directed cephalad, in a transverse plane, to identify the outflow tract as it exits the LV (Figure 14B). Once the left outflow tract is identified exiting the ventricle, the transducer is rotated 45° which confirms the integrity of the ascending aorta, aortic arch and a portion of the descending aorta (Figure 14C). Once the aortic arch is identified, the transducer is rocked towards the fetal head to identify the main pulmonary artery perpendicular to the ascending aorta as it exits the RV (Figure 14D).

Option 2. Identification of the continuity between ascending aorta, aortic arch and descending aorta using the three-vessel-and-trachea view reference for rotation of the transducer

Once the 4CV is identified when the interventricular septum is perpendicular to the ultrasound beam (Figure 15A), the screening examination outlined in the ISUOG guidelines describes directing the ultrasound beam cephalad, in a transverse plane, to identify the 3VTV which demonstrates convergence of the ductus arteriosus with the transverse aortic arch. In this view, the transverse arch is parallel to the ultrasound beam (Figure 15B). By rotating the transducer 90°, the aortic arch can be identified (Figure 15C).

ROLE OF COLOR AND POWER DOPPLER

Color and power Doppler (C/PD) ultrasound are different imaging modalities that identify blood flow in the vessels and the heart. The advantages of C/PD during the screening examination are as follows: (1) identification of shunting ventricular defects not identified with 2D ultrasound because of the grayscale properties of lateral resolution (Figure 16, Video 8), and (2) identification of tricuspid or mitral regurgitation (Figure 17, Video 9), as well as abnormal flow imaged in the 3VTV which can demonstrate aortic or pulmonary stenosis with reversed flow of the compromised outflow tract from the ductus arteriosus (Figure 18, Video 10).

EVALUATION OF FETAL HEART RATE

When an irregular heart rate occurs during the screening examination, the type of rhythm disturbance must be identified. While both pulsed Doppler and M-mode ultrasound have been used to identify the type of rhythm disturbance, the easiest method is M-mode ultrasound.

• Assessment of the atrial rate. This is accomplished by placing the M-mode cursor perpendicular to the atrial wall. This will identify premature beats, premature beats with block, bradycardia and tachycardia (Figure 19A).
• Assessment of atrioventricular rate. The easiest method is to place the M-mode line through the atrial wall and ventricular wall or the M-mode line through the atrial wall and the aortic valve using color Doppler ultrasound imaged in the left outflow tract (Figure 19B,C). Clues to determine the nature of the arrhythmia can also be assessed by examining the real-time image. Video 11 illustrates premature atrial contractions, paroxysmal atrial tachycardia and heart block.

IDENTIFICATION AND SIGNIFICANCE OF A PERICARDIAL EFFUSION

The ISUOG guidelines state the following regarding a pericardial effusion, “A small amount of pericardial fluid is commonly seen during the second and third trimesters (≤2 mm in thickness, at end-systole) and is a normal finding. Some views may also reveal a small hypoechogenic rim around the fetal heart, and care should be taken not to mistake this for a pericardial effusion.”¹⁰ The above statement is not entirely correct and requires further elaboration so those performing a screening examination of the heart understand the evolution of a pericardial effusion and its significance. Identification of a pericardial effusion has the following characteristics compared to a hypoechogenic rim:

• A hypoechogenic rim or echo dropout often is present and may be confused with a pericardial effusion. However, if the pericardium, pericardial fluid, epicardium, and full thickness of the myocardium are identified, then the “hypoechogenic rim” can be differentiated from a pericardial effusion.
• Identification of the full thickness of the myocardium is essential because the hypoechogenic rim is part of the myocardium and results from the curvature of the muscle fibers of the myocardium in which echoes are not reflected to the transducer, resulting in a black area which can be confused with a pericardial effusion which is external to the myocardium.

Figure 20 illustrates the simultaneous presence of a pericardial effusion along the right ventricular wall and a hypoechogenic rim in the left ventricular wall. To separate the hypoechogenic rim from an effusion, color or power Doppler can be used (Figure 21).

Pericardial fluid is commonly observed at the atrioventricular (AV) junction in systole for both the RV and LV and is a normal finding. However, it should not extend along the right or left ventricular walls during systole or diastole (Figures 20 and 21). A pericardial effusion, when present, occurs almost exclusively along the RV wall and not the LV unless hydrops is present or there is LV pathology. A pericardial effusion evolves through the following stages:

• The pericardium and epicardium separate during systole, beginning at the AV junction and dissects towards the apex of the ventricle.
• As the pericardial effusion increases in size, it is present both during systole and diastole.

A pericardial effusion in the second trimester is associated with aneuploidy as well as increased risk for fetal anemia and viral infections.^22,23

The 2-mm rule is misleading and has been promulgated from a study published in the 1990s in which the authors thought the hypoechogenic rim was a pericardial effusion.²⁴ In a study identifying ultrasound markers for trisomy 21, a pericardial effusion was detected in 19% of fetuses with trisomy 21 and in only 2.4% of 2000 controls.²² Therefore, in the second trimester, a pericardial effusion is not common, and if present, indicates an increased relative risk (10.02 (95% CI, 3.82–26.29)) for trisomy 21.²³

A pericardial effusion observed in the third trimester is often associated with placental dysfunction as manifest as a decreased abdominal circumference <10th centile, fetal growth restriction, and/or oligohydramnios. In addition, a pericardial effusion may be one of the first signs of fetal anemia. In my experience, a pericardial effusion of any size has clinical significance in both the second and third trimesters of pregnancy when defined by the above anatomical criteria and should not be confused with hypoechogenic dropout of the myocardium.

CLUES TO ASSIST THE EXAMINER TO IDENTIFY FETUSES WITH CONGENITAL HEART DEFECTS

The non-cardiologist who performs a screening examination is not expected to provide the final diagnosis of a CHD but to identify changes in the screening examination anatomy that would suggest a cardiac defect is present. Following detection of abnormality in the screening views, the patient should be referred to a specialist who can perform fetal echocardiography and counsel the patient regarding the diagnosis and outcome of the detected anomaly. The screener should consider asking the following questions:

• Is the heart axis in the 4CV normal or shifted to the right or left? An abnormal axis has been associated with conotruncal malformations, and lung malformations such as a sequestered lung or cystic adenomatoid malformation, as well as right- and left-sided diaphragmatic hernias (Figure 22).

  

  22

  Abnormal cardiac axis (<25° or >65°), as defined by the ISUOG guideline.¹⁰ (A) Fetus with D-transposition. (B) Fetus with tetralogy of Fallot. (C) Fetus with an endocardial cushion defect.

• Is the size of the heart in the 4CV increased in area or width? Previous work has shown that the increased size of the 4CV is associated with CHDs (Figure 23) as well as other maternal and fetal diseases (Table 1).^17,25

  

  23

  Cardiomegaly demonstrating that the end-diastolic width, length, area and circumference are increased in size as manifest by the z-score values and corresponding z-score percentiles.

  1

  Fetal conditions associated with cardiomegaly. Adapted from DeVore et al.¹⁸

  Affected structure/condition		Abnormality
  Four-chamber view
  	Ventricles	Aneurysm
  	Tricuspid valve	Tricuspid valve regurgitation Ebstein malformation Tricuspid valve dysplasia Tricuspid valve atresia
  	Mitral valve	Mitral valve regurgitation Mitral valve atresia
  	Cardiomyopathy	Myocardial dysplasia or non-compaction Unspecified
  Outflow tracts
  	Aortic valve	Absent aortic valve Critical aortic stenosis
  	Pulmonary valve	Pulmonary valve hypoplasia/atresia Pulmonary valve regurgitation
  Heart rate
  	Arrhythmia	Congenital heart block
  Peripheral vessels
  	Ductus venosus	Agenesis
  	Vein of Galen	Aneurysm
  	Umbilical vein	Aberrant Varix
  	Arteriovenous fistula	Intracranial Pulmonary
  Other fetal/placental problem
  	Fetal anemia	Parvovirus Bart’s hemoglobinopathy
  	Viral infection	Cytomegalovirus
  	Placenta	Chorioangioma
  	Liver	Hemangioendothelioma
  	Thyroid	Goiter
  	Spine	Sacrococcygeal teratoma
  	Lymphatic system	Lymphangioma
  	Connective tissue	Marfan syndrome
  	Mucopolysaccharidosis	Type II (Hunter syndrome)
  	Abdomen	Ascites
  	Chromosomes	Trisomy Tetrasomy
  	Fetal drug exposure	Indomethacin

• Are the atrial chambers of similar size and are the ventricular chambers of similar size or is there disproportion with one chamber appearing to be larger than the other? Disproportion is one of the most common findings in fetuses with hypoplastic RV and LV, and coarctation of the aorta, as well as in fetuses with growth restriction (Figure 24).

  

  24

  Chamber disproportion. (A) This is a fetus with a hypoplastic left ventricle (LV) demonstrating significant disproportion between the right ventricle (RV) and LV and the right atrium (RA) and left atrium (LA). (B) This fetus had a hypoplastic RV as the result of severe tricuspid stenosis. While there is significant disproportion between the ventricular chambers, the atrial chambers are equal in size. 

• Do the right and left ventricular wall thicknesses appear to be increased or disproportionate in width? If one ventricular wall is thicker than the other ventricular wall, then the examiner has to consider that there may be outflow tract stenosis or increased resistance resulting in hypertrophy of the affected ventricular chamber (Figure 24B). Enlargement of both ventricular walls has been observed in fetuses with growth restriction and cardiomyopathy.
• Is the ventricular septum normal size or does it appear to be enlarged? An enlarged ventricular septum has been associated with maternal diabetes and fetal macrosomia as well as structural malformations and fetal growth restriction (Figure 25). A simple method to determine the size of the ventricular septum is to measure the end-diastolic or end-systolic area as described in this chapter using the calculator (Supplement 2 – Septal Calculator).

  

  25

  Septal hypertrophy in a fetus with growth restriction. (A) This illustrates the mid-chamber transverse width at the 40th percentile and the length at the 99th percentile. (B) Enlarged end-diastolic measurement of the ventricular septum.

• Does the ventricular septum appear to be intact? When examining the septum for defects, the best orientation is when the septum is at 45° to the ultrasound beam because it maximizes axial and lateral resolution. If the septum is parallel to the ultrasound beam, artifactual dropout may occur suggesting a ventricular septal defect which may not be present and is the result of echo dropout. If the septum is perpendicular or tangential to the ultrasound beam, then because of lateral resolution, the septal defect may not be identified (Figure 26A,B, Video 12). In this situation, color Doppler will demonstrate shunting of blood across the septum (Figure 26C).

  

  26

  Shunting ventricular septal defect (VSD). (A) Grayscale image with the septum perpendicular to the ultrasound beam. The VSD  is not observed in this plane because of the imaging properties of lateral resolution. (B) Grayscale image with the septum using the combination of axial and lateral resolution which does not demonstrate the VSD. (C) Color Doppler demonstrating a VSD with blood shunting from the LV to the RV.

  12

  Shunting ventricular septal defect observed only with color Doppler ultrasound (different case from that in Video 8).

• Do the mitral and tricuspid valves appear to open normally and have equal excursion during ventricular diastole? When the ventricular or atrial chambers appear to be disproportionate, then the examiner should evaluate the size of the mitral and tricuspid valve openings. This can be done from the real-time image or the M-mode recording directed perpendicular to the septum (Figure 27A,B).

  

  27

  Abnormal atrioventricular valve in a fetus with an endocardial cushion defect. (A) Normal four-chamber view demonstrating opening of the tricuspid and mitral valve leaflets (arrows) during ventricular diastole. (B) Corresponding M-mode tracing at the level of the atrioventricular valves during diastole and the interventricular septum separating the tricuspid (red) and mitral valve (green) leaflets. (C) Four-chamber view demonstrating an endocardial cushion defect consisting of a ventricular and ostium primum septal defect. (D) The M-mode demonstrates a single atrioventricular valve (blue) opening and closing. ASD, atrial septal defect; AV, atrioventricular valve; LA, left atrium; LV, left ventricle; LVW, left ventricular wall; MV, mitral valve; RA, right atrium; RV, right ventricle; RVW, right ventricular wall; TV, tricuspid valve; VSD, ventricular septal defect.  

• Does the insertion of the septal leaflets appear to be offset, with the tricuspid valve inserting lower, towards the apex, than the mitral valve? Absence of the offset has been associated with trisomy 21 and endocardial cushion defect as well as Ebstein’s anomaly (Figure 27C,D, Video 13).
  13

  Endocardial cushion defect.

• Does the foramen ovale flap move within the left atrial chamber normally or is there minimal excursion from the interatrial septum? Abnormal movement of the foramen ovale valve has been recognized with coarctation of the aorta, as well as hypoplastic left ventricle (Figure 28).

  

  28

  Ventricular and atrial disproportion in a fetus with coarctation of the aorta. The left ventricle (LV) and left atrium (LA) are smaller than the right ventricle (RV) and right atrium (RA).

•  Is one or both pulmonary veins observed entering the left atrium? If at least one pulmonary vein is observed, then the examiner can exclude complete anomalous pulmonary venous return (Figure 12).
•  While the 4CV may appear to be normal, (Figure 29A, Video 14) the question should be asked 'Does the size of the aorta at the level of the left outflow tract view appear to be increased in size or does it straddle the interventricular septum?' While a septal defect associated with tetralogy of Fallot, double outlet RV or LV, or truncus arteriosus may not be easily identified during the screening examination, an enlarged aorta is a clue that one of these anomalies may be present (Figure 29B,C, Video 14).

  

  29

  Tetralogy of Fallot. (A) Normal four-chamber view. (B) Left ventricular outflow tract with an enlarged aorta that straddles the ventricular septal defect (VSD). (C) Rotated left ventricular outflow tract (see Figure 14) demonstrating the aortic arch (*), enlarged aorta, short-axis view of the right pulmonary artery (RPA), and the ventricular septal defect. (D) Right outflow tract three-vessel view demonstrating a short-axis view of the enlarged aorta, and small pulmonary artery with a bifurcation.

  14

  Tetralogy of Fallot

•  Is the pulmonary artery smaller than the aorta when examining the three-vessel view? If the pulmonary artery appears to be smaller, one should suspect pulmonary underdevelopment associated with tetralogy of Fallot or other pulmonary artery abnormalities such as stenosis (Figure 29D, Video 14).
•  Does the aortic arch appear to be normal by imaging the ascending aorta, transverse arch and descending aorta? If the vessel bifurcates immediately after exiting the LV, this is a classic sign of D-transposition of the great arteries (Figure 30).

  

  30

  D-transposition of the great arteries. (A) Four-chamber view. (B) Left outflow tract view demonstrating bifurcation of the main pulmonary artery as it exits the left ventricle (LV). (C) Right outflow tract view demonstrating the aorta originating from the right ventricle. AV, aortic valve; LA, left atrium; LPA, left pulmonary artery; MPA, main pulmonary artery; RA, right atrium; RPA, right pulmonary artery; RV, right ventricle; SVC, superior vena cava; T, trachea.

•  Does the 3VTV converge as the vessels enter the aorta or are they separated? If the vessels are separated by the trachea, which lies between the vessels, this is associated with a right-sided aortic arch or other arch anomalies (Figure 31).

  

  31

  Right-sided aortic arch. (A) Four-chamber view. (B) Left outflow tract view. (C) Right outflow tract view. (D) Three-vessel-and-trachea view demonstrating parallel ductus arteriosus and transverse aortic arch with the trachea separating the two vessels.

CONCLUSION

This review has attempted to provide a guide as to how the examiner could approach the screening examination of the fetal heart. Instead of listing different malformations, the anatomical features of the screening examination have been reviewed and questions posed about the anatomical structures that would provide clues that a malformation could be present. Video 15 is a summary of the “enhancements” recently suggested for the ISUOG screening guidelines.¹⁵

PRACTICE RECOMMENDATIONS

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