SAN FRANCISCO--The combination of nuchal thickness measurements and fetal echocardiography can effectively screen for congenital heart defects, according to two studies presented at the annual meeting of the Society for Maternal-Fetal Medicine.
A standardized nuchal thickness measurement and a four-chamber view, both taken on ultrasound at 14-24 weeks' gestation, were independent predictors of congenital heart defects and complemented each other to improve diagnostic accuracy in a study of 1,893 fetuses, Dr. Ray 0. Bahado-Singh reported at the meeting.
Prenatal ultrasound to obtain a four-chamber view of the heart is the most widely used tool for detecting. congenital heart defects, but its sensitivity in the general population is limited, six previous studies have shown.
One 1994 study found a sensitivity as low as 21% when the four-chamber view was used.
In the current study, investigators converted nuchal thickness measurements to multiples of the median and standardized them for biparieral diameter measurement, comparing an individual fetus's measurement to standardized measurements, for a normal fetal group to calculate the individual's risk for heart defects. They compared these. estimations and the estimated risk based on findings from the four-chamber view with actual outcomes.
A review of maternal and pediatric charts showed that 6% of patients had congenital heart defects.
Nuchal thickness measurements were 42% sensitive and 77% specific in detecting congenital heart defects. The four-chamber view was 39% sensitive and99% specific for heart defects, said. Dr. BahadoSingh, director of maternal-fetal medicine and professor of ob.gyn. at the University of Cincinnati.
An integrated approach using both nuchal thickness and four-chamber view results proved 50% sensitive for heart defects with a false-positive rate of 5%. Accuracy improved with the earlier ultrasounds taken at 14-16 weeks: The integrated algorithm was 57% sensitive for heart defects, with a false-positive rate of less than 1%, he added.
A 2002 survey of U.S. maternal-fetal medicine specialists found that 80% already perform midrrimester nuchal thickness and heart evaluations to assess the risk for Down syndrome. "This suggests that our proposed integrated algorithm could easily be incorporated into clinical practice," he said.
Measuring nuchal thickness fits the features of a screening test: The technique requires little expertise, is not timeconsuming, and fits within the scope of current clinical practice, Dr. Bahado-Singh said. He called. for large studies of-low-risk populations-to-see-if the algorithm improves early detection of congenital heart defects.
In a separate study, 4 of 23 karyotypically normal fetuses with increased nuchal thickness on ultrasound at 11-14 weeks' gestation were found to have congenital heart defects on subsequent fetal echocardiography and neonatal cardiac evaluation, for a prevalence of 17%, Dr. Lami Yeo reported in a poster presentation.
The investigators prospectively collected nuchal thickness measurements and compared them with results of echocardiograms performed. at a median age of 24 weeks' gestation. The 23 fetuses had a nuchal thickness of 2.5 mm or greater, with a median thickness of 3 mm.
The 17% prevalence of cardiac defects suggests that any karyotypically normal fetus with increased nuchal thickness on first-trimester ultrasound should undergo detailed fetal echocardiography said Dr. Yea of the Robert Wood Johnson Medical School, New Brunswick, NJ.
A normal fetal echocardiogram reduces the risk, of congenital heart defect to approximately 4%-5%, he added.
The echocardiograms spotted heart defects in three of the four fetuses that had them, resulting, in a sensitivity of 75%. Echocardiograms missed one atrial septal defect but detected another. It also found one case of ventricular septal defect and multiple defects in the fourth patient: an atrio ventricular canal defect, double, outlet right ventricle, transposition of great vessels, and aortic hypoplasia.
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