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Fruit of the Womb
Fruit of the Womb

Invasive Diagnostic Testing after Reassuring First Trimester Screening for Aneuploidy?

Attached is a comment from a reader who has written to me before because of a history of recurrent early pregnancy losses. She is now pregnant, has successfully gotten through first trimester, and has had very reassuring combined risk assessment for aneuploidy. She is now wrestling with the decision regarding whether or not she should undergo an amniocentesis for fetal chromosomal analysis anyway, mostly because of her age. In the end, she will have to make that decision herself, but in my response, I offer a perspective, occasionally, overlooked, to her and to others who are facing this decision...

Dr. T - I wrote to you a few months ago on your recurrent loss blog regarding my two 2007 1st trimester losses - I followed your advice to see a good RE (reproductive endocrinologist), we found impaired glucose tolerance, I started metformin, and I am happy to report that I am 15 1/2 weeks pregnant with what seems to be a healthy baby! So, thanks for that.

Here's my new question: I just turned 39. I had a NT done, and my risk for Downs is 1/2000 and my risk for Trisomy 18 is 1/3700 - which is reassuring. I scheduled an amnio anyway, because I am 39, and because of the possibility of the chromosomal problems with my lost pregnancies last year. Now, I am a week away from the amnio, and I am getting paranoid about the risk from the amnio of losing this baby. What I don't quite understand is how a history of previous losses impacts the risk of amnio. Does it make a difference if your previous losses were not spontaneous miscarriages, but missed ones? I was ok with my decision to have an amnio until yesterday, and now I can't get past the thought that something bad might happen. I know that my doctor doesn't care either way if I do the test or not, but I don't want to talk myself out of (or into) something if I am being overly cautious. Thanks in advance.

Tue Jan 22, 09:25:00 AM 2008

Kenneth F. Trofatter, Jr., MD, PhD said...

To Liz Jan 22: Liz, I am not going to tell you what to do. But, let me put this in perspective. The risk of the amniocentesis in experienced hands is still about twice that of your a priori risk for having a baby with Down syndrome or trisomy 18 (and probably several other chromosomal abnormalities as well) based on your first trimester screening results. In less experienced hands, the amniocentesis risk can be 10 times your first trimester screening risk! With those odds, if you did happen to be the 1 in 1000 (or 1 in 200) who lost their baby as the result of the amniocentesis, the overwhelming odds are that you will lose a completely NORMAL baby.

You are doing very well, you have been through a lot to get to this point, odds are this baby is normal, and you are 39 years old. You may not have many more opportunities if this one is lost. One option to consider, rather than jumping into the amniocentesis now, is to simply have a genetic sonogram done at 18-20 weeks. If that is normal, your a priori risk (based on the first trimester screening results, NOT your age) is reduced by at least another 50% (I generally quote folks 60-80%). So, answer me does a 1 in 4,000 risk sound to you? If something really suspicious is seen at that point such as poor fetal growth, congenital heart defect, or a major marker for aneuploidy (and I am NOT talking about an echogenic intracardiac focus, or even a choroid plexus cyst alone), you could still opt for the amniocentesis with a FISH (fluorescent in situ hybridization) analysis for the more common types of chromosomal abnormalities. This can give you highly reliable results within 72 hours. Using first trimester screening, coupled with this approach, we have not missed a chromosmal abnormality in more than three years, nor lost a baby from an amniocentesis. By the way, CONGRATULATIONS! Again, best wishes to you and please let us know how you do with the pregnancy!
Dr T

Tue Jan 22, 05:27:00 PM 2008
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