Routine Sonography of Fetal Heart Advocated.
Such an exam can help identify structural heart defects, evaluate arrhythmias, assess ventricular function, and flag possible chromosomal abnormalities such as trisomies 21, 18, and 13, which have a strong association with congenital heart anomalies, according to Dr. Benacerraf, professor of ob.gyn. and radiology at Harvard Medical School, Boston.
"The hardest ultrasound examination to do," fetal echocardiography, has been shown to be equally effective in detecting abnormalities in low- and high-risk patients, she said at the conference sponsored by the American Institute of Ultra sound in Medicine.
Indications for a fetal echocardiogram include a family history of congenital heart defects, poorly controlled diabetes, maternal drug use of lithium or anticon vulsants, maternal alcohol use, or a known chromosomal anomaly.
Echocardiography can detect abnormalities in blood flow, such as regurgitation and reverse flow into the aortic root from the ductus arteriosus, which could indicate complete obstruction or a hypoplastic left heart.
Sonographic examination of the fetal heart should not be limited to those at high risk for such disorders, said Dr. Benacerraf, who studied 69 fetuses with con genital heart disease whose mothers had undergone prenatal sonography at 18 weeks or later.
At the time of referral for sonography, 39 of the fetuses had been diagnosed as high risk and 30 as low risk for cardiac disorders.
"There was no difference in the sensitivity of detecting cardiac anomalies between the two groups," she said. Of the 69 fetuses with structural cardiac abnormalities studied, the test identified 57 (83%).
When a standard four-chamber view and outflow views with color flow Doppler imaging on all fetuses were used, anomalies that were consistently identified included hypoplastic left and right heart, single ventricle, tetralogy of Fallot, transposition of the great arteries, and Ebstein's anomaly.
When the four-chamber view alone was used, 42% of existing fetal abnormalities were missed, including transposition of the great arteries and tetralogy of Fallot.
"Since 43% of the 69 fetuses with heart defects were referred for low-risk indications, systematic sonographic examination of the fetal heart should not be re served only for those at high risk," Dr. Benacerraf concluded.
Noting that transvaginal scans of the fetal heart are often attempted as early as 12-14 weeks' gestation, Dr. Benacerraf warned that "you can start out with a nor mal heart at 16 weeks and end up with critical aortic stenosis." She recommends repeating the sonographic examination after 18 weeks if it is incomplete.
The finding of an abnormal cardiac axis is one of the markers that should prompt further evaluation, she said. In another one of Dr. Benecerraf's studies, 75 fetuses with heart defects diagnosed on prenatal sonogram had a mean cardiac axis of 56 degrees. The frequency of cardiac rotation was greatest in fetuses with truncus arteriosus, Ebstein's anomaly, pulmonic stenosis, coarctation of the aorta, and tetralogy of Fallot. "The cardiac axis test is helpful in detecting the difficult anomalies," Dr. Benacerraf said.