First-Trimester Fetal Echocardiography

Published on 07/06/2015 by admin

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4 First-Trimester Fetal Echocardiography

Lisa K. Hornberger

I. HISTORICAL BACKGROUND

A. Normal first-trimester heart

1. Fetal cardiac anatomy was initially documented by Dolkart and Reimers in 1991, who assessed 52 fetuses ranging in gestational age from 10 to 14.9 weeks.

2. Normal first-trimester Doppler flow patterns were initially documented by Wladimiroff and colleagues in 1991. They assessed left and right ventricular inflow and outflow velocities in 30 fetuses ranging in gestational age from 11 to 13 weeks.

B. First early diagnosis of fetal heart disease

1. In 1990, Gembruch and colleagues described a case of left atrial isomerism with atrioventricular (AV) septal defect and AV block at 12 weeks of gestation.

2. Also in 1990, Bronshtein and colleagues diagnosed tetralogy of Fallot at 14 weeks of gestation.

C. Transvaginal versus transabdominal approaches

1. Earlier data suggested that transabdominal imaging was less useful than transvaginal imaging for first-trimester screening.

a. Transabdominal fetal ultrasound allowed assessment of the four chambers in less than 20% at 13 to 14 weeks (Catanzarite and Quirk, 1990).

b. Transvaginal ultrasound at 13 to 14 weeks (Dolkart and Reimers, 1990; Johnson et al, 1992; Hornberger and Benacerraf, 1995).

    (1) A four-chamber view was seen in more than 75%.
    (2) Great arteries were documented in more than 50%.

2. More recent data suggest that transabdominal and transvaginal approaches complement each other.

a. Haak and colleagues (1992) attempted a full cardiac assessment, including a four-chamber view, aortic root, long axis of the aorta, pulmonary trunk, and great artery crossover.

    (1) At 11 to 12 weeks’ gestation, they had 20% success.
    (2) At 13 to 14 weeks’ gestation, they had 92% success.

b. Huggon and colleagues, 2002.

    (1) Successful fetal heart assessment when crown-to-rump length was more than 60 mm.
    (2) Maternal body size was also important for transabdominal imaging.
       (a) At body mass index (BMI) of 23.6 kg/m2, imaging was successful.
       (b) At a mean BMI of 26 kg/m2, imaging was not successful.

3. Doppler assessment.

a. Hornberger and Benacerraf (1995) studied the frequency with which Doppler flow can be demonstrated and found significant improvement with gestational age.

b. Leiva and colleagues (1999) studied first-trimester changes in flow patterns.

    (1) They studied 48 pregnancies at 6 to 12 weeks.
    (2) The inflow signal was monophasic until 10 weeks, then biphasic with an increasing E wave.
    (3) Isovolumic contraction was 20% of the cycle at 6 weeks, then decreased to 0 after 12 weeks.
    (4) Isovolumic relaxation time was 16% throughout early gestational age.

II. LIMITATIONS

A. Reduced image resolution

1. Fetal size is a critical factor. Because this is a rapid period of general fetal growth, every week helps.

2. Fetal distance from the transducer significantly limits resolution. Transvaginal imaging should not be considered unless the fetus is less than 7 cm from the cervix.

3. Uterine anatomy can interfere with image resolution, particularly for the transvaginal approach.

4. As a result of such limitations, ventricular septal defects, AV septal defects, and more subtle conditions such as tetralogy of Fallot with milder pulmonary outflow obstruction may be missed.

B. Greater fetal activity at earlier gestational ages

C. Fetal position

1. Fetal position is still an important factor, particularly with transvaginal imaging, given limited range of motion of the transducer.

2. Mobility of the fetus helps with the early assessment because the fetus can change position significantly several times during the examination.

D. Potential for progression or development of lesions later in gestation

1. Left and right heart obstructive lesions.

a. Pulmonary and aortic valve stenosis.

b. Coarctation of the aorta.

2. Cardiomyopathy.

3. Rhabdomyomas.

4. Dysrhythmia.

E. Safety issues

1. The operator must be aware of the acoustic output of instruments used.

a. Thermal and mechanical indices must be within recommended levels.

b. These indices provide relative risk of producing thermal or cavitation effects.

2. Risks may be greater during embryogenesis (<10 weeks; Campbell and Platt, 1999).

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