Measuring the thickness of the fetal nuchal translucency (NT) at 11 to 13 + 6 weeks is an effective way to screen for chromosomal defects. Increased NT has also been associated with major cardiac defects as well as numerous fetal malformations and genetic syndromes. In this study, the prevalence of major cardiac defects was determined by fetal echocardiography in 6921 fetuses with a normal—or presumably normal—karyotype. The study was done at a median gestational age of 20 weeks. The most common indications were increased NT thickness on the 11 to 13 + 6 scan, a perceived need to estimate the risk of chromosomal abnormality, and a history or family history of fetal defects. Most often, the echo study was done transabdominally. Either chorionic villus sampling or amniocentesis demonstrated a normal fetal karyotype, or a phenotypically normal infant was born alive. Cases with other than cardiac fetal abnormalities were excluded.
Major cardiac defects were found in 132 fetuses, a prevalence of 19.1 per 1000. The prevalence increased with fetal NT thickness. It was 4.9 per 1000 when NT thickness was below the median; 8.7 per 1000 with an NT thickness between the median and less than the 95th percentile; 18.2 per 1000 for an NT thickness between the 95th and 99th centiles; and then exponentially to 35.2, 64.4, and 126.7 mm, respectfully, for NT measurements of 3.5–4.4 mm, 4.5–5.4 mm, and 5.5 mm or greater. There was no apparent difference in the distribution of NT thickness values for different types of cardiac defects.
The authors believe that combining a first-trimester NT thickness measurement with a second-trimester four-chamber echocardiographic view will promote the antenatal detection of major cardiac defects in fetuses with a normal karyotype.
Harris Birthright Research Centre for Fetal Medicine, King’s College Hospital Medical School, London, U.K.
Ultrasound Obstet Gynecol 2005;26:154–157