Nowadays, it is quite simple to detect pregnancy without going to the physician and undergoing a series of invasive procedures. Home pregnancy tests have made this process both private and straightforward. They work on the principle of hormone quantification: the test strips are labeled with a specific molecule that can detect the presence of human chorionic gonadotropin, or hCG, in the urine. Once the level of this hormone surpasses a certain threshold, it can be detected with one of these kits.
While these tests are user-friendly, they can have some problems. For example, one of the most common problems with pregnancy tests is their expiration date. In this article, you will learn all about expired pregnancy tests, such as their accuracy, and get answers to some key questions you may have.
Do pregnancy tests ever really expire?
Many pregnant women are not even aware that pregnancy tests, like all other deteriorating goods, have an expiry date. However, pregnancy tests for home use do have a best-before date, which is often printed on the container or outer packaging.
Why do home pregnancy tests expire?
As mentioned earlier, pregnancy tests contain a chemical that can detect hCG levels in urine. This chemical is called hCG antibody and consists of two arms that identify and bind to the hCG in the urine. However, after a certain period of time, the antibody arms break down and become invalid. This is the most common reason for the expiry date of a pregnancy test.
When does a pregnancy test become invalid?
It depends on the brand of pregnancy test, but the general shelf life is between two and three years from the date of manufacture. The cheaper tests expire more quickly than the more expensive ones. In fact, expensive tests are often still usable after the expiration date, but cheaper ones may expire before the set date due to low quality production. In any case, it is safest to use pregnancy tests only a few months before their expiration date.
Will an expired pregnancy test kit still work?
An expired pregnancy test kit may still work in rare cases, but the result is what is called a false positive. A positive result from an expired test basically means that the test claims you are pregnant when in fact you are not.
The next question you may be asking is: can an expired pregnancy test give a false negative result? The answer is yes. Expired tests are also less sensitive enough to detect the hormone hCG, resulting in a false negative result. In this case, even if you are pregnant, the test will show that you are not. These results are especially common if the test has been kept in a warm and humid room for an extended period of time.
These two situations can quickly escalate and cause unnecessary problems! Therefore, always check the expiration date of the pregnancy test before you buy/use it. If you accidentally use an expired test kit, don’t fret about the results of an expired test. Just get a new test kit and get the correct result.
What to expect when you use an outdated pregnancy test kit
As mentioned earlier, expired pregnancy tests can give you four results: a true positive, a true negative, a false positive, and a false negative. However, false results can also occur for other reasons.
A false-positive test can be due to the following reasons:
- Ectopic or non-viable pregnancy, in which the zygote does not implant in the uterus but attaches elsewhere. If you experience bleeding and extreme abdominal pain at any time during your pregnancy, please see your doctor immediately.
- Recording errors when performing the test include performing it too early or too late, or reading the lines on the test strip incorrectly. Please read the instructions included with the pregnancy test before doing so.
- Fertility medications sometimes contain hCG, which can give a false-positive result.
- A miscarriage can cause a false-positive result because the level of hCG in the blood is still high weeks or months after a miscarriage.
A false-negative test result can have the following causes:
- Errors in recording, e.g., not following the test strip lines, using the first or last urine drop instead of collecting the specimen from the midstream.
- Dilution of the urine, which means that the hCG level in the urine is also low. Ideally, you should use morning urine, which has a much higher concentration.
- If you did not wait long enough after the first missed period, this could mean that the hCG level in your body has not yet risen sufficiently.
What to do if you use an already expired test to confirm pregnancy?
Home pregnancy tests are not 100% accurate and must always be confirmed by your doctor. In particular, using expired tests can cause fluctuating and erroneous results.
The results of an expired pregnancy test depend mainly on three key factors:
- The quality of the test itself, which plays an important role in the accuracy of the expired test.
- The amount of degraded anti-hCG antibody, the chemical used to gauge the concentration of human chorionic gonadotropin, the pregnancy marker, in the urine.
- The presence or absence of the pregnancy itself.
Only your doctor can determine your pregnancy beyond any doubt. So if you have any concerns about the results of your home test, you should see him as soon as possible.