How Likely is it to Get a False Positive on a Pregnancy Test?

April 4, 2019

There is nothing that can make two minutes feel like two hours as taking a pregnancy test. Regardless of what you hope the results will be, the desire to know immediately can be overwhelming. The thought of the possibility of getting a false positive can cause you to become more anxious in an already stressful situation.

So, how likely is it to get a false positive on a pregnancy test?

Accuracy of At-Home Pregnancy Tests

At-home pregnancy tests work by placing a plastic stick into your stream of urine. The instructions then have you wait a specific of time, for their sensor to determine whether there is any human chorionic gonadotropin (hCG) in your system. This is a hormone produced by the placenta after a fertilized egg implants on the uterus. Home pregnancy tests usually include a control line that’s always present. If there’s hCG in your urine, a second line will appear above it. Sometimes, instead of two lines, you’ll see a plus sign, or a “pregnant” or “not pregnant” message on the display window.

The vast majority of at-home pregnancy tests are fairly accurate, as long as you take them after the first day of a missed period. While some brands claim they can detect pregnancy before then, hCG can take a few days to enter your bloodstream and urine. That said, when taken correctly, store-bought pregnancy tests are about 99% accurate.

What Causes of a False Positive on a Pregnancy Test?

So what causes that 1% of false results? There could be several reasons.

1. User Error

It’s not enough to just pee on a stick. You have to read the instructions thoroughly and follow them exactly as suggested. Some require you to take the test as soon as you wake up in the morning, since that’s the time of day when urine is most concentrated. There are also time requirements: Leave the stick in the stream of urine for as long as the test manufacturer suggests you do so. Read the expiration date on the box. Give it a few days for your body to actually detect hCG if there’s any.

2. Evaporation Lines

Here’s yet another reason to read the instructions carefully: Some tests require that you wait two minutes. Others require you to wait up to five minutes. If you leave the stick sitting around longer than what’s required in the instructions, as urine evaporates, a faint line may appear on the screen, on top of the control line. If you’ve read the instructions, you’ll (a) know the exact time to check for results, and (b) know exactly what a positive line will look like, so that you don’t confuse it with anything else.

3. Fertility Treatments

If you’re undergoing fertility treatments, be aware that some medications include synthetic hCG shots, designed to stimulate the production and release of mature eggs. Some of these medications include Pregnyl, Noveral, and Ovidrel.

4. Early Miscarriage

It’s possible for a woman to experience a miscarriage even before she realizes that she’s pregnant. This is called a chemical pregnancy, and it occurs when a fertilized egg detaches from the uterus soon after implantation. However, since there was implantation, there may still be traces of hCG in your urine.

5. Medical Conditions

Urinary Tract Infections (UTIs), ovarian cysts, kidney disease, pituitary gland disorders, gestational trophoblastic tumors, and certain cancers, may cause a woman to create hCG, which would lead to a false positive pregnancy test.

Call OB-GYN Women’s Centre of Lakewood Ranch for More Information

At OB-GYN Women’s Centre of Lakewood Ranch, we provide a variety of services for every woman. Whether you’re planning for a family or trying to avoid conception, we can help you.

Call us today to schedule an appointment.