Prenatal Diagnostic Testing: CVS, amnio, cordo Flashcards

1
Q

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?

A

All women

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2
Q

What is the time period that Chorionic Villus Sampling (CVS) can be done?

A

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

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3
Q

What is the danger of performing CVS prior to 9 weeks gestation?

A

associated with limb anomalies in the fetus

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4
Q

How is CVS performed?

A
  • under ultrasound guidance
  • transcervically or transabdominally (depends on position of placenta)
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5
Q

What kind of pain is expcted for transcervical vs transabdominal CVS?

A

transcervical: uncomfortable because of full bladder
transabdominal: pain that is well tolerated. due to manipulation of need to suction CV

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6
Q

What is the procedure related risk for CVS?

A

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

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7
Q

What are the recommendations for patients for the rest of the day after their CVS or amnio?

A
  • take it easy
  • no heavy lifting, nothing >30 lbs
  • no strenuous exercise, defer to Dr if pt wants more info about exercising
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8
Q

What are the considerations for multiples?
- Monochorionic twins
- Dichorionic twins
- Higher order multiples

A
  • 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
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9
Q

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?

A

The easiest fetus to access will be reduced. It is made clear to pateints up front that they do NOT get to choose.

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10
Q

What is the main advantage to CVS?

A

early diagnosis (can be done in the 1st trimester)
this is especiailly true for molecular genetic testing

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11
Q

What are disadvantages to CVS?

A
  • 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)
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12
Q

What is the risk for confined placental mosaicism with CVS?

A
  • 1-2% of samples have confined placental mosaicism
  • this is only relevant for aneuploidy, not for single-gene molecular testing
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13
Q

What is a significant limitation of performing CVS on a pregnancy from IVF that had PGT-A testing?

A

-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.

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14
Q

What are the limitations regarding testing for fragile X via CVS?

A
  • 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
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15
Q

In general, a lot of testing is done simply becuase it is able to be done earlier. What testing is considered the gold standard?

A

amniocentesis

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16
Q

What is the limitation of performing CVS after a positive NIPT result?

A
  • 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
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17
Q

What is amniotic fluid?

A

fetal urine

18
Q

When is amniocentesis performed?

A

16 weeks or later
(sometimes attempted at 15 weeks)

19
Q

How is amniocentesis performed?

A
  • abdominally with US guidance
  • 1-2 tablespoons of fluid collected (there are fetal skin cells in the amniotic fluid)
20
Q

Does an aminocentesis depleat the amniotic fluid?

A

No
It is replaced in about 2 days
It does not depleat the baby’s amniotic supply

21
Q

What is considered an early amnio and what are the associated difficulties?

A
  • before 15 weeks
  • not offered at URMC
  • there may not be fusion between the chorion (part of the placenta) and amnion (amnotic membrane) yet. This can lead to an unsuccessful procedure due to tentiing. This is not a danger to the baby.
  • Additonally, there is some data to suggest that delayed fusion of the amnion and chorion is an independent risk factor for aneuploidy
22
Q

What is the complication rate for amniocentesis?

A

1 in1,000
- rupture of the amniotic sac
- infection
- induction of labor

23
Q

How does the explanation of risk of amnio change depending on gestational age?

A
  • prior to 24 weeks: 1 in 1,000 risk that could lead to miscarriage
  • after 24 weeks: 1 in 1,000 risk could lead to early labor and delivery
  • note: must be careful about ordering amnio after 24 weeks for babies with anomalies that could be impacted by small size/early delivery, ex: if newborn surgery may be needed early delivery could complicate things greatly and make the surgery impossible
24
Q

How do they tell that they are getting a sample from each baby when there are multiple fetuses?

A
  • sampling needle will need to pased multiple times
  • dye can be injected in the sac to help confirm that second tap is unique (if the second pass is blue instead of straw, you know you tapped same sac twice)
25
Q

What are the advantages of amnio?

A
  • sampling fetal cell line so diagnostic
  • lower risk than CVS
  • can check for viral DNA to check for infection such as CMV
  • ONTD screening
26
Q

Why are we able to detect ONTDs on aminocentesis?

A
  • 95% detection rate
  • If AF-AFP is high - reflex to detection of acetylcholinesterase (AchE)
  • If AchE is present = ONTD
  • this is because AchE is produced by nerve cells and should not be in the amniotic fluid.
27
Q

What would be the main reason an AchE test would be falsely positive?

A

bloody tap

28
Q

What is the main disvantage of amnio?

A

timing - delay in potential diagonsis (can get to 24 weeks quickly - remember, what is purpose of test?)
- turnaround times for testing are:
- karyotype = 2 weeks
- microarray = 2 weeks
- single-gene testing = 2-6 weeks
- WES STAT = 2 weeks

29
Q

Cordocentesis/Pericutaneous Umbilical
Blood Sampling (PUBS)
What is this and when is it done?

A
  • the only way to collect fetal blood during pregnancy
  • after 17 weeks

GCs don’t do consents for these procedures at URMC

30
Q

Why is PUBS done?

A
  • to assess for fetal anemia: this is suspected when hydrops develops later in pregnancy
  • treat fetal anemia with transfusion
  • adminster medications
31
Q

What are the risks of PUBS and why is it not used for genetic testing?

A
  • 5% risk to lead to loss
  • not used for genetic testing because of higher risk
  • brachycardia in fetus is also a risk
32
Q

What are some maternal infections of concern to obstetrics?

A
  • HIV: if viral load is undetectable probably okay
  • Hepatitis C: check with DR
33
Q

What is the concern regarding maternal blood type for obstetrics?

A
  • Mom who is Rh -
  • If Mom is Rh- she will be given Rhogram to prevent interaction with fetus. This would be an issue if the baby is Rh+
  • All Moms that are Rh- get the shot because PUBS would need to be done to check baby.
34
Q

Common questions from patients:

Will it hurt the baby?

A

CVS: no, we only worry about potential complications
amnio: we tell them no, but it is possible to basically poke the baby with the needle but they’ll be fine

35
Q

Common questions from patients:

Will it hurt me?

A

transabdominal CVS: maybe
rest: just uncomfortable

needle for amnio thinner than for phlebotomy (blood draw)

36
Q

Common questions from patients:

Do they give something for the pain?

A

No.
Can only numb surface but pain is from muscle cramping so we can’t do anything helpful.

No ibuprofen while pregnant!

37
Q

Common questions from patients:

Can I have something for anxiety before the procedure?

A

Yes, one time anxiety meds are usually prescribed if requested. If referred from outside OB office their office will have to order it.

38
Q

NYS requires signed consent for all genetic testing. Providers can sign verifying patient has given consent. True or False?

A

TRUE

39
Q

Sample size warning and the consent forms for CVS and amnio. What is the difference?

A

CVS: There is a warning about sample size being too small, can talk to DR about repeating potentially.
Amnio: No warning about sample size since they will see sample size in real time.

40
Q

What are the detection rates for aneuploidy and spina bifida with amnio?

A

aneuploidy = about 100%
spina bifida = about 95%