NUCHAL TRANSLUCENCY SCREENING / COMBINED SCREEN FOR FETAL ANEUPLOIDY
The primary disadvantage is
This test integrates
the 3 risk components that have been found to be effective in detection
of fetal Down syndrome
The combined screen for fetal aneuploidy requires 3 components, as outlined by the Fetal Medicine Foundation.
RESULTS AND INTERPRETATION OF RESULTS
Results should return within a week or sooner. The results will be faxed directly to the referring physician office. If the patient has had a formal counseling session, the genetic counselor or physician may phone the patient directly, if previously approved by the referring physician and patient.
Like 2nd trimester
screening, results are typically returned as "Within normative range" or
"positive". The basis for these designations depends on the
overall calculated risk, based on the combination of maternal age,
ultrasound measurements, and maternal biochemistry. The risk of fetal
Down syndrome in a 35 year old woman (1:270) is typically used as the
threshold for making this determination, so that all risks less than
this will be termed "within normative range" and all risks higher than
this are termed "positive". Note that the positive indication does NOT
indicate that the fetus has Down syndrome, only that the risk is
considered to be high enough that the woman may want to consider further
It is far more likely that the fetus is completely normal. For example,
a risk of 1:200 would be considered "positive" but the odds are that
199 of 200 cases the fetus will be normal.
Statement by the Fetal
Fetal Medicine Foundation promotes screening for Down syndrome at 11-14
weeks by Nuchal Translucency or a combination of nuchal translucency and
maternal serum biochemistry.