NT of 4 mm or more warrants chorionic villus sampling.
In such cases, there is no added benefit in performing serum screening or in using the nuchal translucency (NT) value for developing a risk assessment algorithm because a measurement of at least 4 mm is indicative of extremely high aneuploidy risk, said Dr. Malone, professor and chair of the department of obstetrics and gynecology at the Royal College of Surgeons in Ireland and Rotunda Hospital, Dublin.
The finding is based on an analysis of data from more than 36,000 of the women who participated in the National Institute of Child Health and Human Development-funded First and Second Trimester Evaluation of Risk (FASTER) trial.
Data used in this analysis were from women who underwent both NT measurement and serum testing. Of the 32 FASTER participants who had a simple NT measurement of at least 4 mm, 1 in 3 had aneuploidy and 1 in 11 had fetal demise. The lowest final first-trimester risk quoted for any of these patients based on NT measurement alone was 1 in 8, and for those with aneuploidy, the lowest risk quoted was 7 in 8. No patient in this group had a final risk assessment reduced to a more reassuring level (1 in 100 or less) by the addition of serum markers, Dr. Malone said.
Of the 128 patients with an NT measurement of at least 3 mm, 1 in 6 had aneuploidy, 1 in 40 had cardiac malformation, and 1 in 30 had fetal demise.
The lowest risk quoted in these patients was 1 in 1,479, and the lowest risk quoted in aneuploidy cases in this group was 1 in 2. About 10% of these patients had the final assessment reduced to a more reassuring level with the addition of serum markers.
In contrast, 60% of those with a 2 mm or greater simple NT measurement had the final risk assessment reduced to a more reassuring level with the addition of serum markers.
An NT measurement of 4 mm or greater is an indication for immediate chorionic villus sampling, and a measurement of 3 mm or greater is an indication for strong consideration of chorionic villus sampling, Dr. Malone concluded. The majority of patients with a measurement of less than 3 mm will benefit from the addition of serum markers, he said.
In addition to the previous key FASTER trial finding showing that a subset of first-trimester fetuses could be identified as being at especially high risk for adverse outcomes based on the presence of septated cystic hygromas on NT screening, this new finding shows that there is also a subset of patients in whom NT measurement alone is an indication of especially high risk.
This finding could be of great practical value for clinicians performing NT-based screening, he said.
BY SHARON WORCESTER
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|Title Annotation:||News; nuchal translucency|
|Publication:||OB GYN News|
|Date:||Mar 1, 2006|
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