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We just received our amnio results and were given the unexpected news that our baby girl is positive with Trisomy 21. I have heard so many stories that others were prenatally diagnosed with a Down syndrome baby, and when they went full-term with the pregnancy their baby was fine. I want to be sure there were no mistakes in the lab. Am I just being paranoid?”
I’m really sorry that you’ve received a prenatal diagnosis of Trisomy 21.
Unfortunately, the happy-ending stories we hear about “wrong” prenatal test results are typically based people not understanding the difference between a screening test and a diagnostic test.
Screening tests like the maternal alpha-feto protein test (AFP or MAFP), triple screen, quad screen, nuchal fold translucency, etc. do not diagnose fetal anomalies. They only serve as indicators that chances of a problem existing are statistically higher than normal, and that actual diagnostic tests such as the CVS or amniocentesis and/or high level ultrasounds performed by maternal-fetal specialist are called for.
When people tell these stories about their co-worker’s cousin’s neighbor’s sister’s friend who got a bad prenatal diagnosis, refused to listen to the doctors, prayed a whole bunch and gave birth to a bouncing miracle baby, the “tests” in question were invariably non-diagnostic screening tests.
Screening tests can have a false-positive rate of five percent or more. In other words, one out 20 mothers getting a screening test could end up with a false positive result. It’s not surprising that a few of them then refuse actual diagnostic testing and go on to have healthy babies. Nor is it surprising that we’re subjected to these magical miracle “the prenatal test was wrong” stories. It’s human nature: people just love dramatic “happy endings” that defy expectations—even when they’re not actually true.
On the other hand, the amnio is a diagnostic test and it is between 99.4% and 100% accurate. Even if you go with the low-end to the 99.4% accuracy rate, most people will still get secondary confirmation of fetal defects from one or more a high-level ultrasounds. There would have to be a lot of reckless malpractice going on for a healthy pregnancy to get misdiagnosed with serious chromosomal or fetal anomalies.
We would never suggest anyone consider ending a wanted pregnancy based on a screening test results alone. By the same token, we don’t suggest ignoring the results of actual diagnostic tests.
I wish I could give you more hope than that, but when one is making a decision this momentous, it is always best to deal in facts.