Couple questions about amniocentesis

[cbrons]

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Couple questions about amniocentesis - I hope these make sense:

- For amniocentesis, is there is a slight risk of sampling mosaic cells?

- My notes also say that early amniocentesis has a ~5% chance of leading to miscarriage. Really? Why in the world would it even be performed early then?

I am also pretty unclear as to how the procedure might lead to miscarriage in the first place. Is the extraction of ~20 ml of fluid considered a lot?

 

[diehardobgyn]

The risk we generally quote is 1 in 300. It is performed early for a few reasons, mostly when patients want to have definitive diagnosis regarding chromosomal or other genetic abnormalities. This is particularly useful for patients who may consider termination depending on diagnosis. Many people elect not to have the procedure specifically because of the risk of miscarriage. As far as miscarriage goes, its not the amount of fluid that leads to miscarriage. There are a few things that can: injury to the fetus with the needle, infection of the amniotic fluid that leads to preterm labor and delivery, and bleeding that can also lead to miscarriage. It may also lead to spontaneous membrane rupture which subsequently leads to miscarriage if the needle hole doesn't seal.

 

[Global Disrobal]

There is a slight chance for sampling mosaic cells.

General practice is to draw off 2 cc first, which will remove contaminant cells, and then the usual 15-20 cc.

I quote my patients 1:600, which is the best available data (and 1:200 for CVS). The risk predominantly lies in the second trimester amnios and not so much the third trimeter lung maturity taps. With respect to the former, it's PPROM (which has the highest chance of spontaneous seal compared with traditional PPROM or high leak), chorio, bleeding, etc.

For your studying, the single most important point should be the patient's Rh status.

With respect to your last question, 20cc is not considered substantial; however, this of course depends on the clinical situation. In may second trimester oligohydramnios cases where the fluid is already low, I often offer my patients a placental biopsy (CVS) rather than a fluid unless absolutely necessary, or tap another fluid cavity (bladder in cases of bladder obstruction, pleural in cases of hydrothorax, etc.). The fetus will likely regenerate the fluid as it's the fetal urine.

Hope this helps. Best of luck!

 

[cbrons]

Thanks a lot, I appreciate the responses