False Negatives Reported After 5 To 7 Weeks

Pregnancy tests are pretty accurate — right? Well, a recent study has found that nearly all of the most popular brands of tests used by hospitals become less accurate the more pregnant you are.

Pregnancy test

Photo credit: Don Farrall/Photodisc/Getty Images

While most pregnancy tests used by hospitals are accurate the first month after conception, a recent study has found that nine of the 11 most popular brands used by hospitals don't do so great at detecting pregnancy after that time period. This can be a huge problem. Why?

Pregnancy tests at the hospital

If you're pregnant and you don't know it, and the hospital staff doesn't know it, then you may be administered medication that is unsafe for your baby. Also, you may undergo procedures that are also not recommended during pregnancy, such as X-rays or CT scans. Having a false negative may also result in not being properly diagnosed with an ectopic pregnancy, which can be life-threatening.

Nine of the 11 tests that were studied showed that past five to seven weeks of pregnancy, the ability to detect hCG dropped off significantly. The reason is that when a pregnancy approaches this stage, urine concentrations of an hCG variant known as hCG beta core fragment begins to rise, which can interfere with hCG detection.

The two tests that worked the best were the BC Icon 20 and the Alere. They found that two of the other tests (the OSOM and the Cen-Med Elite) were so affected by the hCG beta core fragment that the risks of false negatives were too high for acceptable use.

What does this mean?

The researchers say that health care staff needs to be aware that this is a problem, and that if quantitative beta hCG blood testing is available, then that needs to be the test used because the problem doesn't exist in that type of test. They also urge that pregnancy test manufacturers work to establish a better test, and in the meantime, include warnings that false negatives may occur if used past a certain timeframe.

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