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Pregnant. What are the risks of doing amniocentesis procedure?

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Hi. I'm 18 weeks pregnant, 36 years old and I have a big dilema regarding the decision to do amniocentesis. NT = normal, first trimester blood screening 1:5000 risk of Down sx, 16 wkx GA: 1:1000 risk of Down sx ( as far as I know the risk for my age is about 1:170). In view of the newest guidelines of ACOG do I need to do an amniocentesis; I'll have the structural anatomy ultrasound to be done in 1 week from now.
What is the best decision to take in my case? First pregnancy, no hx of miscarriages or abortions, no hx of genetic abnormalities in my or my husband's family; what will be the benefits and the risks of doing an amniocentesis in my case ?
Posted Fri, 7 Dec 2012 in Women's Health
Answered by Dr. Asra Ishtiaq Ahmed 1 hour later
Hello there.

Thanks for writing.

First trimester screening with blood test and nuchal translucency (NT) are effective screening tests for down's syndrome.

Those found to be at increased risk of having a baby with Down syndrome with first trimester screening are offered the option of Chorionic villus sampling or mid trimester amniocentesis.

There is cut off point (risk assessment) in screening tests to decide if you need a diagnostic (amniocentesis) test.
In some hospitals the cut off is 1 in 150 while in others it is 1:250. The cut off is not decided by age alone.

Considering your results of the blood tests done in first trimester and at 16 weeks GA, you fall into screen negative or unlikely to be carrying a baby with Down's, THOUGH IT IS NOT IMPOSSIBLE.

Considering ACOG guidelines, it advises option of diagnostic testing (amniocentesis) regardless of age.
The factors which influence this decision are family or personal history of birth defects, the risk that the fetus will have a chromosome abnormality or an inherited condition and the risk of pregnancy loss from an invasive procedure.

Maternal age of 35 is no longer used by itself as a cut off to determine who should be offered screening versus invasive diagnostic testing.

Thus as per the guidelines. your family, personal history and your reports, you may not require an invasive test.


Structural anatomy ultrasound for congenital anomalies has to be done irrespective of your decision for amniocentesis as this is mandatory in all pregnancies.

Benefit of going for an amniocentesis would be if your blood screening test was false negative. It is 98% effective in diagnosing downs syndrome.

Risks to you can be risks involved with the procedure which include miscarriage, infection and premature labor.
Mild side effects after the procedure include irritation at the puncture site, abdominal cramps and leaking of fluid per vagina.

I hope I have answered your queries.

Wishing You All the Best.

Take care.
Above answer was peer-reviewed by
Follow-up: Pregnant. What are the risks of doing amniocentesis procedure? 15 minutes later
Thank you very much for your answer.

Are there any other benefits in doing amniocentesis, other than that of diagnosing Down syndrome ( I understand that there is still a 2% chance of missing it, even after amniocentesis); are other chromosomal anomalies routinely tested through amniocentesis?

Thank you,
Answered by Dr. Asra Ishtiaq Ahmed 33 minutes later
Hello there.

You are most welcome for queries.

Yes other anomalies like neural tube defects and spina bifida (spinal defects) can be diagnosed with amniocentesis. Also certain congenital infections in baby can be diagnosed.
But these are also not routinely tested. Its only when the risk factors for the same are present.

Lung maturity of the baby is estimated through amniocentesis when a premature delivery is expected.

Take care.
Above answer was peer-reviewed by
Follow-up: Pregnant. What are the risks of doing amniocentesis procedure? 26 minutes later
Thank you again for your prompt answer.

Can Harmony prenatal test, replace the amniocentesis? ( this test is done by Ariosa laboratories and is rated as having 99% accuracy)

Thank you very much,
Answered by Dr. Asra Ishtiaq Ahmed 1 hour later
Hello there.

Thanks for writing back.

The harmony prenatal test has to be compared to first trimester blood screening tests you got.
This because it is also a screening test.

The difference is that it HAS HIGHER SENSITIVITY ( TRUE DETECTION RATE) than the first trimester screen test.

Also it is based on a different principle where in maternal blood is estimated for relative amount of chromosomes.

Chormosome number detection helps in knowing the risk to having syndromes of fetal anomalies associated with abnormal chromosome number. (for example trisomy 21 seen in downs syndrome)

Thus using a more sensitive test can reduce the need of doing a diagnostic test like amniocentesis by reducing the number of false negatives.

Take care.
Above answer was peer-reviewed by
Follow-up: Pregnant. What are the risks of doing amniocentesis procedure? 3 hours later
Thank you for answering all my questions.

I'm reading a lot of good reviews about Harmony prenatal test. It is specified that its sensitivity can reach 97-100% and specificity 97.9-100%, while for amniocentesis I found similar numbers. In view of these numbers why is this considered still a screening test (I understand that the test itself is looking at the chromosomes, found in fetal cells / DNA material found in maternal blood) compared to amniocentesis ?

Thanks again,
Answered by Dr. Asra Ishtiaq Ahmed 41 minutes later
Hello there.

Thanks for writing back.

It can not be considered a diagnostic test since it is done on the mother and not on the fetus. It utilizes cell free DNA in maternal blood for detecting chromosomal abnormality compared to amniocentesis which utilizes fetal cells in amniotic fluid.
Thus amniocentesis is more specific and diagnostic.

The only advantage of harmony test is that it being more sensitive and more specific than the other screening tests, it fulfils the criteria of being a good screening test which include safety, sensitivity, specificity, easy and affordability. Thus the need for a diagnostic test can be avoided due to lower false results.

Considering the risks associated with amniocentesis, it can be a wiser option to go for a highly sensitive and specific screening test to avoid risks associated with diagnostic procedure of amniocentesis.

I hope I have answered your query.

take care.
Above answer was peer-reviewed by
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