How Do Pregnancy Tests Work?

Three minutes doesn’t sound like a long time until you’re waiting in the bathroom with a plastic stick in your hand, watching to see if a second line appears. 

Knowing what a pregnancy test measures can help you understand the importance of timing and whether you can trust your result.

You don’t have to sort through this on your own, either. The Cline Center offers no-cost, confidential pregnancy testing and ultrasounds in Jackson, and you can schedule an appointment to get a clear answer from a licensed medical professional.

What a Pregnancy Test Looks For

Every pregnancy test, whether you buy it at the drugstore or take it at a clinic, searches for one hormone: human chorionic gonadotropin, usually shortened to hCG.

According to the Mayo Clinic, your body starts producing hCG after a fertilized egg attaches to the lining of the uterus, a process called implantation. The placenta begins forming at that point, and the placenta makes the hormone.

If the concentration of hCG in your urine is at least 25 mIU/mL, a pregnancy test will return a positive result. 

Why Timing Changes Your Result

In early pregnancy, hCG levels rise quickly, roughly doubling every 2 to 3 days. A test taken a day or two after a missed period usually has a high enough concentration of hCG to trigger a positive result.

Ovulation shifts from month to month, though, and a fertilized egg can implant at different times. Both of those variables change when your body starts producing hCG, and irregular cycles add another layer of uncertainty, making a missed period harder to pin down.

The time of day also plays a role. Testing first thing in the morning, when your urine is most concentrated, gives the test the best chance of finding the hormone.

If your pregnancy test is negative and your period hasn’t arrived, it could turn positive with a little more time.

Reading the Test Correctly

The method you use depends on the type of pregnancy test you bought. 

A midstream stick has an absorbent tip that you hold directly in your urine stream for a few seconds. Whereas a test strip goes into a small cup of urine you’ve already collected, dipped to the fill line, and pulled back out. A cassette test comes with its own dropper, and you squeeze a few drops into the little well on the plastic case.

All three work similarly, and the result appears in the window a few minutes later. Look for a plus or minus sign, one line or two, or the words “pregnant” or “not pregnant.”

Checking too early or too late could lead to an incorrect result, so it helps to set a timer for the exact wait time printed in the directions. Most tests also include a control indicator, and if that line or symbol never appears, the test itself isn’t working, and you’ll want to try a new one.

Can a Test Be Wrong?

Home tests often advertise 99% accuracy, but they differ in how well they detect a pregnancy right after a missed period. A false negative can happen when you test too soon, check the window before the result is ready, or take the test after drinking lots of fluids.

False positives are rare. When they do happen, the cause is usually an early pregnancy loss, a fertility medication that contains hCG, or an underlying issue involving the ovaries or menopause.

If your test comes back negative and your period still doesn’t start, the Mayo Clinic suggests testing again about a week later or talking with a medical professional.

What a Positive Test Doesn’t Tell You

A positive result confirms hCG in your urine, but it can’t tell you how far along you are, whether the pregnancy is growing normally, or whether the pregnancy is located in the correct area. 

Those answers come from an ultrasound, and The Cline Center offers ultrasounds following a positive pregnancy test. An ultrasound performed by a licensed medical professional can confirm that the pregnancy is located in the uterus, estimate your gestational age, and identify if there are any complications like an ectopic pregnancy that need immediate attention.

Pregnancy Testing at The Cline Center

You don’t have to decide anything the moment you learn your result. At The Cline Center, medical-grade pregnancy testing happens on-site and costs you nothing, and you’ll have the chance to sit down with an advocate afterward to talk through what your result means.

Schedule your no-cost, confidential appointment, or call us at (601) 487-1064.