Tuesday, September 1, 2009

False Positives

A false positive pregnancy test is when the test says that you are pregnant but actually you are not. False positive pregnancy tests are rare - though there are instances and conditions where they can occur.

I have had very few clients report a false positive. Probably the most heartbreaking thing to happen while you are TTC. You yearn for that second line, to get it and then have all your baby dreams come crashing down because of it being a false positive.

Most false positives are due to those nasty evap lines that some (if not all tests get).

What is an EVAP line?

Evaporation ("evap") lines result with the test's antibody strip just looks slightly
different than the space around it. There is a line of antibodies (usually made
from mouse cells) in the Control and Test section. The Control line binds with any liquid and turns pink (or blue, in tests using blue dye.) The Test line turns pink only if the pregnancy hormone is detected. If not, the moisture passes over this strip and does not turn pink. It may, however, become more visible when the light hits the moisture on the strip-- it may appear gray, colorless, like a "dent" in the test, or like a "ghost line." It may appear at any time-- as soon as the urine hits it, after a few minutes as the test absorbs the moisture, or after the 10-minute time limit. It may appear when the test is drying, or after it has dried. It may disappear as the test is drying, or after the test has dried, or not disappear at all.

The simple fact is that there is always "something there" that is slightly visible--
it's simply the antibodies on the test that would turn pink in the presence of hCG.When the test becomes wet, or as it dries, or after it dries, the antibody strip may become more visible. Therefore, all tests may have them. It is not a defect, it's just how tests are made.


Other reasons for getting a "false positive" could be:

1)Chemical Pregnancy
A chemical pregnancy is basically an early miscarriage. The fertilized egg does not implant successfully into your uterus. These days HPTs have a high sensitivity to hCG, picking up the smallest amount. You might get a faint positive only to have AF arriving a day or two later.

2)Chemical Interference
If you are under going fertility treatment which includes the trigger shot for ovulation, you are advised not to test too early in case of getting a false positive. Since these drugs have the hCG hormone in them, and will show "positive" on a test. It takes on average about 10 days after the shot to "work out" of your system. So try holding out on testing until at least 11/12dpo.

During my 3 year journey of TTC, I think I had about 3 of these "false positives". 1 of which I was convinced it was a chemical pregnancy. The other 2 I'm sure were due to evap lines showing up after the time limit.