Prenatal Diagnostic Testing: CVS, amnio, cordo Flashcards
Both ACOG and the Society for Maternal-Fetal Medicine have recommended that invasive diagnostic testing as well as screening for
aneuploidy should be available to whom?
All women
What is the time period that Chorionic Villus Sampling (CVS) can be done?
11w0d-13w6d gestation
- In rare instances, a couple of our MFMs
might dip into the 14th week
- We do not performed CVS prior to 11
weeks gestation
What is the danger of performing CVS prior to 9 weeks gestation?
associated with limb anomalies in the fetus
How is CVS performed?
- under ultrasound guidance
- transcervically or transabdominally (depends on position of placenta)
What kind of pain is expcted for transcervical vs transabdominal CVS?
transcervical: uncomfortable because of full bladder
transabdominal: pain that is well tolerated. due to manipulation of need to suction CV
What is the procedure related risk for CVS?
1%
includes risk for anything from procedure until delivery that could lead to loss of pregnancy
patients are asked to take it easy the day of the procedure
What are the recommendations for patients for the rest of the day after their CVS or amnio?
- take it easy
- no heavy lifting, nothing >30 lbs
- no strenuous exercise, defer to Dr if pt wants more info about exercising
What are the considerations for multiples?
- Monochorionic twins
- Dichorionic twins
- Higher order multiples
- Monochorionic twins: one placenta to sample = easy!
- dichorionic twins: 2 placentas potnetially to sample, but they may not be distinct though
- Higher order multiples: may not be able to obtain samples from all placentas because of access
When considering multifetal reduction, CVS will be attempted on as many placentas as possible. If aneuploidy is detected on a sample, that fetus can be selectively reduced. If aneuploidy is not detected, how is it determind which fetus will be reduced?
The easiest fetus to access will be reduced. It is made clear to pateints up front that they do NOT get to choose.
What is the main advantage to CVS?
early diagnosis (can be done in the 1st trimester)
this is especiailly true for molecular genetic testing
What are disadvantages to CVS?
- confined placental mosaicism (1-2% risk) (only relevant for aneuploidy, not single gene molecular testing)
- complication risk is higher than for amniocentesis
- can not screen for ONTDs (amnio can)
- maternal cell contamination can complicate results (we do not test for this at URMC)
What is the risk for confined placental mosaicism with CVS?
- 1-2% of samples have confined placental mosaicism
- this is only relevant for aneuploidy, not for single-gene molecular testing
What is a significant limitation of performing CVS on a pregnancy from IVF that had PGT-A testing?
-PGT-A: performed on biopsy of the trophectoderm
- CVS: performed on the cytotrophoblast cell layer of the chorionic villi. This is what NIPT is looking at as well.
- embryologically these are very similar, meaning you would essentially be repeating a test that was already done
- we can still order this testing, but it important for patients to undersatnd this limitation. Amnio would be a better test for these patients.
What are the limitations regarding testing for fragile X via CVS?
- prelimiary PCR results can only be reported if unabiguous - testing is very sensitive to maternal cell contamination
- final results by Sourthern can be inconclusive due to methylation timing in gestiation, so methlation testing may be needed to confirm distinguishing between large premutation and small full mutation
- amnio can be offered for clarification
In general, a lot of testing is done simply becuase it is able to be done earlier. What testing is considered the gold standard?
amniocentesis
What is the limitation of performing CVS after a positive NIPT result?
- these tests are both placental testing - so it’s repetitive
- if testing results align it is considered diagnostic
- if mosaicism is present at any point, amnio is indicated