Should you take the AFP/triple screen test?
Mar 13 '00 (Updated Jun 11 '01)
The Bottom Line Did you know that there is absolutely no way to get a "false positive" result on the AFP/triple screen test? Even though your friends think it happened to them!
"Oh, I'd never take the AFP test!" my friend said. "I've known so many women who had false positives - they had abnormal test results and went on to have perfectly healthy babies!" She assumed their test results were "wrong," but she was the one who was wrong.
Should you take the AFP test? This is a question that many pregnant women will have to answer. But many, if not most, pregnant women cannot make an informed decision because they do not understand how the test works and what it tells you (and what it doesn't tell you). For example, though you've probably heard stories of women who had a "false positive" test result, you may be surprised to know that you cannot get a "false positive" result from this test. Why? Read on.
What is it?
The AFP (alpha-feto protein test) measures the amount of AFP, a substance produced by the placenta and fetus, in a pregnant woman's blood. The AFP is often part of a group of tests called the "triple screen," which also measure human chorionic gonadotropin (HCG) and unconjugated estriol (UE3).
What does it do?
Based on the amounts of these substances in your blood, the AFP and triple screen test can give you the statistical risk of having a child with certain disorders (Down syndrome, neural tube disorders, etc.) The test can not tell you if your unborn child actually has one of these disorders, it can only give you the odds. If your test indicates an increased risk, you will probably be offered further testing, such as amniocentesis or a detailed "level 2" ultrasound. These tests can further narrow down the likelihood that your child will have any particular disorder (and in fact, usually rule it out - most women who have an abnormal result on the test go on to have a normal baby).
So why is there no such thing as a "false positive" result?
Because the AFP and triple screen do not give you a positive or negative result. An abnormal result is not a positive. All they can do is indicate your level of risk.
For example, let's say that because of your age you have a 1 in 500 chance of having a child with Down syndrome. Does that mean it will or will not happen? Neither. It simply indicates the likelihood of it happening. Your test results do the same thing. If your triple screen test indicates a 1 in 80 chance of having a child with Down syndrome, it may be an abnormal result, an increased risk, but it is still not a positive or negative result. You still have a 79 in 80 chance of having a normal child, and if you do, it doesn't mean the test was wrong. For the same reason, there is no such thing as a "false negative" result. The test cannot guarantee you are having a healthy child.
Then why take this test?
Women with an abnormal result often find that the next step is amniocentesis. Amnio carries its own risks, and is not recommended for every pregnant woman. The AFP and triple screen can "screen out" those women who would be less likely to benefit from amnio and "screen in" those who might need it. Some women know they would refuse amnio under any circumstances and therefore might not benefit by the AFP/triple screen. But other women need the information. Some may plan to abort a severely disabled child. Others want to be prepared, emotionally and practically, for the birth. For example, a child with a neural tube defect may require a c-section delivery or may need surgery immediately after (or even before) birth, which would affect your birth plans.
So what should I do?
Only you and your partner can make that decision. But you should ask yourself if the benefit is worth the risk. Are you at risk for any of the disorders that can be detected? If you get an abnormal result, would you undergo amnio or would you refuse it? If you're only going to spend the next 20 weeks worrying about the result, you might be better off skipping the test altogether. But make that decision based on the facts, not the myth of the "false positive" result.
And a final note... here's a very good opinion on the subject from someone who has been there and done that:
http://www.epinions.com/./kifm-review-5EB7-EB34215-38EE3CB6-prod4
(Note: This opinion was edited 12/29/2000)
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Member: Tracy
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