Increased fetal nuchal translucency thickness at 10–14 weeks of gestation may be sensitive in screening for major abnormalities of the heart and great arteries

DI A G N O S IS

Increased fetal nuchal translucency thickness at 10`14 weeks of gestation may be sensitive in screening for major abnormalities of the heart and great arteries Hyett J, Perdu M, Sharland G, Snijders R, Nicolaides KH. Using fetal nuchal translucency to screen for major congenital cardiac defects at 10d14 weeks of gestation: population based cohort study. BMJ 1999;318:81d85

OBJECTIVE To assess the utility of measuring fetal nuchal translucency thickness in screening for major abnormalities of the heart and great arteries at 10–14 weeks of gestation. DESIGN Population-based cohort study. SETTING Single fetal medicine center in London, UK. PARTICIPANTS 29 154 singleton pregnancies with a live fetus at 10–14 weeks of gestation, with a crown-rump length of 38–84 mm. Pregnancies with chromosomal abnormalities and those that ended with spontaneous miscarriages were excluded. Screening was performed at a median of 12 weeks of gestation (range 10–14) and the median maternal age was 34 years (range 15–48 years). DESCRIPTION OF TEST AND DIAGNOSTIC STANDARD Fetal nuchal translucency thickness associated with subcutaneous edema in the neck region was measured by transabdominal ultrasonography or, if visualization was poor, by vaginal ultrasonography. The diagnostic standard was pregnancy outcome diagnosed either antenatally, at post-mortem examination or postnatally, as obtained from the maternity units, general practitioners or the patients themselves. MAIN OUTCOME MEASURES Sensitivity, specificity, positive predictive value and negative predictive value. MAIN RESULTS Major defects of the heart and great arteries were identified in 50 pregnancies, including 18 diagnosed antenatally, 13 at post-mortem examination, and 19 in livebirths.

Commentary Congenital heart defects occur in 0.8% of the general population. They are important because they may be life-threatening, and because treatment is often difficult, resource-intensive, and unfortunately, not always successful. Prenatal detection of congenital heart defects has therefore become an area of priority in materno-fetal medicine. Data from several authors in the early 1990s have suggested a dismal detection rate for cardiac defects from routine ultrasound screening in the early second trimester, ranging from 2.61 up to 26%2. In contrast, directed scanning for fetal anomalies by specialist centers may enjoy a high rate of success, with 78% of the defects detected in the initial examination at 22 weeks gestation in one recent report (an additional 7% were detected in the third trimester, and only 15% escaped detection).3 The problem may be one of the adequate population screening and referral to the centers of expertise. The article by Hyett et al. addresses the problem of early screening and proposes adding fetal nuchal translucency thickness to the screening protocol. The authors have previously reported an increased prevalence of congenital heart defects in the fetuses with early increased nuchal translucency thickness, and a possible exponential relationship of the congenital heart disease prevalence with the degree of thickness. The present study retrospectively evaluates the utility of this parameter as a screening tool in a large population-based cohort studied at a tertiary care center.

^ 1999 Harcourt Publishers Ltd

The prevalence of major cardiac defects was 1.7/1000 pregnancies. The prevalence of major cardiac defects was 0.8/1000 pregnancies for those with nuchal translucency thickness below the 95th centile, 5.3/1000 for those with nuchal translucency thickness above the 95th centile, and 63.5/1000 for those with nuchal translucency thickness above the 99th centile. A total of 28 of the 50 pregnancies (56%; CI 42–70%) with major cardiac defects were among the fetuses with nuchal translucency thickness above the 95th centile. Sensitivity, specificity, positive predictive value and negative predictive value (95% CI) for two cut-off points (95th and 99th centile) are provided in the following table:

Sensitivity Specificity Positive predictive value Negative predictive value

95th centile

99th centile

56.0% (42.0–70.0) 93.8% (93.6–94.1) 1.5% (1.0–2.1)

40.0% (26.0–54.0) 99.0% (98.9–99.1) 6.3% (3.7–9.0)

99.9% (99.8–100.0)

99.9% (99.8–100.0)

CONCLUSION Including the measurement of nuchal translucency thickness as a screening test for major abnormalities of the heart and great arteries at 10–14 weeks of gestation may increase the detection rate of these defects.

The data show a substantial increase in the prevalence of ‘major’ congenital heart defects in the group of fetuses with increased 14-week nuchal translucency thickness, becoming striking with thickness '99th centile. However, the real value of these findings in a screenings test may be less impressive, as noted from the relatively low positive predictive values of abnormal findings'95th centile. Interpretation of the clinical impact of this screening technique is limited by the retrospective nature of this correlation. Numerous indications are already accepted for performing a directed fetal echocardiogram.3,4 As part of a composite risk index score, increased nuchal translucency thickness may significantly increase the sensitivity of early ultrasound screening for congenital heart defects. A multi-center prospective evaluation of such an index is currently in progress in North America. Paul F. Kantor, MB, BCh Assistant Professor, Pediatric Cardiology McMaster University and University of Toronto, Ontario, Canada

Literature cited 1. Ewigman BG, Crane JP, Frigoletto FD et al. N Engl J Med 1993; 329: 821d827 2. Tegnander E, Eik-Ness SH, Johansen OJ et al. Ultrasound Obstet Gynaecol 1995; 5: 372d380 3. Yagel S, Weissman A, Rotstein Z et al. Circulation 1997; 96: 550d555 4. Eronen M. Arch Dis Chil 1997; 77: F41dF46

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