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Spot heart defects early to increase survival. (Routine Surveillance Inadequate).

CANCUN, MEXICO -- Prenatal detection of congenital heart defects can improve an infant's chance of survival if delivery is then done at a tertiary cardiac center.

But most congenital heart defects won't be seen with a prenatal ultrasound examination unless the fetus is at high risk and comprehensive examinations are done, Dr. Joshua A. Copel said at a conference on obstetrics, gynecology, perinatal medicine, neonatology, and the law.

In the Routine Antenatal Diagnostic Imaging With Ultrasound Study (RADIUS), which during the early 1990s assessed the efficacy of two routine, prenatal ultrasound examinations in low-risk fetuses, the detection rate for congenital heart defects was 0% when examinations were done by primary care physicians, but 23% when the ultrasound examinations were done at tertiary referral practices.

"The standard of care is that routine ultrasound cannot detect most cases of congenital heart disease; even in tertiary practices, only [about] 25% of defects were seen," said Dr. Copel, director of obstetrics at Yale-New Haven Hospital.

On the flip side, the positive predictive value of a putative heart defect seen with ultrasound is about 50%.

The deficiencies of ultrasound for prenatal diagnosis are a problem, because congenital heart defects are not rare but they are very dangerous.

The defects have a prevalence of about 8 in every 1,000 live births. An average obstetrician who delivers about 10 infants a month will deliver one baby with a congenital heart defect about every 20 months. In the United States, congenital anomalies are the No. 1 killer of infants up to 1 year old, causing about 21% of all deaths in this group; about a third of these congenital anomalies involve congenital heart disease.

In general, neonates with congenital heart defects fare better when the defect is known in advance. At Dr. Copel's hospital, for example, the survival rate of 36 neonates who were born with a known heart defect and required a two-ventricle repair was 80%. In contrast, the survival rate among 36 similar neonates whose heart defect was identified only postnatally was 66%.

Data collected at several other tertiary centers around the world show a similar pattern, although the level of benefit from prenatal diagnosis is linked to the type of defect involved and the ability of pediatric surgeons to successfully correct the defect.

A physician's failure to find a congenital heart defect in a fetus by ultrasound is not substandard care. However, a physician who fails to attempt to get a four-chamber view of the heart in a low-risk fetus during an ultrasound examination in the second or third trimester is violating the standard of care, Dr. Copel said at the conference, sponsored by Boston University and the Center for Human Genetics.

An examining physician who is unable to see the heart by ultrasound during the second or third trimester should clearly document this in the patient's file along with the reason for the failure.

For fetuses with risk factors for congenital heart defects, a simple four-chamber view is insufficient. A comprehensive heart examination is needed. When this is done, the rate for detecting defects is 80%-95%.

The newest boost to prenatal screening for congenital heart defects is prenatal examination of nuchal thickening.

"Nuchal translucency will be an important tool in screening for many defects during the first trimester," Dr. Copel said. In one recently reported study involving more than 1,300 pregnancies, a nuchal thickness of 3.5 mm correlated with a 4-fold increased risk of a congenital heart defect, and a nuchal thickness of more than 5.5 mm correlated with a 175-fold increased risk.
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Author:Zoler, Mitchel L.
Publication:OB GYN News
Date:Mar 1, 2003
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