4 First-Trimester Fetal Echocardiography
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.
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).
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.
b. Huggon and colleagues, 2002.
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.
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.
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).