Straightforward answers to
What is rapid prenatal diagnosis?
Fluorescent DNA probes are used to analyze the chromosome makeup of cells obtained from amniotic fluid or a chorionic villus sample (CVS). While not all chromosome abnormalities can be identified by this technique, the majority of common abnormalities can be identified. These include Down syndrome (trisomy 21), trisomy 18, trisomy 13, Klinefelter syndrome (47,XXY), triple-X syndrome (47,XXX), Turner syndrome (45,X) and 47,XYY. The technique is known as interphase FISH, which stands for fluorescent in situ hybridization, or simply as FISH. Our laboratory uses the AneuVysion test, which has been cleared by the FDA for this purpose.When should this be considered?
Sometimes important pregnancy management decisions need to be made quickly, while waiting for a complete cytogenetic result. The following are some of the situations in which a rapid assay may be helpful.What are limitations of rapid prenatal diagnosis?
- Maternal age, serum screening, or ultrasound findings indicates a high risk for an Down syndrome or trisomy 18.
- Prenatal chromosome diagnosis is indicated, but the patient is more than 20 weeks gestation.
- An ultrasound examination in the second or third trimester suggests the fetus has Down syndrome, trisomy 13, or trisomy 18.
- A patient has concern about whether the fetus has a chromosome abnormality; for example, a chromosome problem was discovered in a previous pregnancy.
- This analysis does not screen for all chromosome abnormalities, only missing or extra copies of chromosomes 21, 18, 13, X, and Y.
- Prenatal FISH is not designed to detect chromosome mosaicism, partial chromosome duplications and deletions, or structural rearrangements.
- Although prenatal FISH analysis is highly accurate, irreversible therapeutic decisions should not be made on FISH results alone.
- An additional 5-10ml of amniotic fluid is required for the rapid FISH assay, in addition to the 15-20ml required for conventional chromosome studies. Samples with visible blood may not be suitable for FISH analysis.
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