Quad screen test negative. Could it be false negative??

[saizjj]

My Quad screen testing came back yesterday as negative with a ratio of 1 in 4200 for Trisomy 18. The first trimester screening was 1 in 5000. I was a little concerned when I took the test because it was done past the time it usually is. They did it at 20 weeks and told me it is done between 15-17 weeks. I go in 2 weeks for an echocardiagram of baby's heart and to see if the 2 choroid plexus cysts have gone. the level II US at 19 weeks showed everything else looking good, baby's hand opened and closed, feet looked good, kidneys and amnio fluid were good, baby was on target with growth, but the heart wasn't big enough to look closely at. I know the quad screen can have false positive but does anyone know if there are false negatives??? I just didnt know accuracy, especially since it was done past the usual time.

[newterpmom]

Since the quad screen is just a statistical test, it is certainly possible to have a "false positive" and a "false negative". Please do not worry, though. I put those terms in quotes specifically because in a statistical test, there really is no such thing as a "false positive" or a "false negative", because there really isn't a "positive" or a "negative". When a screening test is done, it is simple looking at the levels of specific hormones in your blood and comparing them to the hormone levels of other pregnant women. They expect the hormone levels to be within a certain range and if the hormones fall outside that range, it can be linked to certain conditions (T18, T21, etc). How far off of "normal" the hormone levels are, results in the statistical result you are given (1 in 200, 1 in 4000, etc.). That number is your result. Some labs will return a "positive" or "negative" verdict, but that is based purely on what your number is. They have a cut off (usually around 1 in 200), and say that any odds higher than that (say 1 in 50) is termed "positive" because at that point the risk of losing the baby due to amnio miscarriage is less than the odds of the baby having the condition tested for.

There are several problems with this method. First, just becoming pregnant means you have a risk of having a baby with a chromosomal abnormality. Whether the odds are 1 in 50 (2% chance) or 1 in 500 (0.2% chance) or 1 in 5000 (0.02% chance), you still have a chance. That means that even if your odds are 1 in 5000, which would be considered "negative", someone is that 1 person. The reverse is also true, if your odds are 1 in 50, which would be considered "positive", it still means that 49 people will have completely normal babies.

Another problem with these tests are that some people do not fall within the "normal" range, even if their babies are perfectly normal (again, it goes back to the 1 in 50 odds, 49 people will have completely normal babies). One of my husband's cousins had odds of 1 in 7 that her baby had T21 (Downs syndrome). He was perfectly healthy.

I know this post is probably confusing, and let me state that I am *not* a medical person (I am an engineer), but I deal with statistics on a daily basis (what are the odds that a part will fail). I actually opted against any screening tests for both my pregnancies because, in my mind, the results would not have meant anything. There is still always a chance, regardless of what the screening tests say. That is why the level II US is a much better diagnostic tool than the tests. CPCs were found on my daughter, but not my son. My son, however, measured large the entire pregnancy, which freaked me out for other reasons. He was born on March 31, 2009 two weeks early and perfectly healthy at 8 lbs, 1 oz.

So, since your baby looks great on the US (hands opening and closing, growth on track, etc.) the odds are she is perfectly healthy.

Good luck!

missie

[saizjj]

thank you so much for your response. the echocardigram is in 1 week and I am ready for it to get here. The baby moves all the time so I am assuming that her being active is a good sign. On the 19 wk ultrasound her all looked great and hands opened and closed. I have what may seem like a strange question, but could that change over time? If her hands open and close as they should now, that shouldn't change on the next ultrasound should it? I just assume if that were a sign it would show early on and not just develop slowly over time. Sorry, I am just being paranoid and overly worried. thanks again.

[newterpmom]

No apologies for being paranoid. You're worried about your baby and that is expected. As to your question, with T18, the clenched fists are a deformity that happens as the fetus develops that *prevents* the hands from being able to open and close. If her hands were able to open and close before, then she is fine with respect to that marker. It isn't something that develops over time.

Best wishes!

missie