How Does a Pregnancy Test Work?

Contraceptives like condoms and birth control aren’t always completely effective, as many people continue to discover. Even when utilizing these methods, it’s still possible for women of all ages to accidentally become pregnant.

Over-the-counter pregnancy tests give women the resources to determine privately whether or not they’re pregnant, with no professional or medical assistance. Therefore, pregnancy tests are a critical step prior to a woman’s decision to receive an abortion or not. In this post, we’ll discuss the fundamentals of pregnancy tests and how they work. 


When to Take a Pregnancy Test

Generally, women take pregnancy tests when they’re experiencing pregnancy symptoms or physical anomalies they can’t explain. However, some may take a pregnancy test if they have doubts about the efficacy of their birth control. Below, you’ll find some of the most common instances you may want to take pregnancy tests:

  • Late period: If you’re sexually active, you should always keep track of your cycle. This is applicable whether you’re using contraceptives or not. While it’s possible to miss a period because of other variables (like stress and diet), it can often indicate pregnancy. Even during pregnancy, women may experience spotting, without full-blown menstrual bleeding.
  • Cramping: Cramping that feels like menstrual cramps can also be a sign of pregnancy, especially when the period doesn’t follow. This is attributed to embryo implantation. If you’re experiencing menstrual cramps that don’t lead to a period, then consider taking a pregnancy test.
  • Breast pain/tenderness: Pregnancy causes the body to generate more hormones (estrogen and progesterone), thus causing accelerated blood flow as well. Because of this, the breasts may feel especially tender, with some degree of discomfort.
  • General Discomfort: While this may seem painfully general, it’s also accurate. Pay close attention to how you feel on a day-to-day basis, especially if you have another reason to believe you’re pregnant. Pregnancy can cause random, spontaneous feelings of sudden nausea, fatigue, and physical reactions to certain foods and aromas, among other things.
  • Failed contraception: Both birth control and condoms are, generally, effective pregnancy prevention methods. Unfortunately, though, they occasionally don’t work as intended. If you have any reason to suspect ineffective contraception, then take a pregnancy test.


How Does a Pregnancy Test Work

Pregnancy tests help determine whether or not a woman is pregnant based on the presence of a specific hormone. This hormone, called human chorionic gonadotropin (hCG), usually indicates pregnancy.

The Primary Factor: hCG Production

After fertilization in the Fallopian tubes, the egg moves into and embeds itself within the uterus. Then, it begins to produce hCG.

Subsequently, this causes the mother to release progesterone, keeping the uterine lining in place. These chemicals are then released in the mother’s urine. 

Zone 1: The Reaction Zone

In the shape of a stick, pregnancy tests detect the presence (or absence) of certain chemicals in the urine. They do so by gradually absorbing the urine as it travels up the stick.

There are three distinct zones in which the stick tests for this hormone. The reaction zone contains absorbent fibers, which have an antibody that attaches itself only to hCG. 

Zone 2: The Test Zone

As the urine continues to travel up the stick, it transports these antibodies over to the second area, the test zone. The test zone contains a unique chemical that reacts with these antibodies, but only when hCG is present.

If this is the case, it subsequently releases a colored dye, creating a colored line on the test strip. If the test does not detect a pregnancy, then no line will form.

Zone 3: The Control Zone

After this critical step, the urine progresses to the control zone, or the third area of the pregnancy test. In this area, there are chemicals that react with the antibodies, whether or not there is hCG present. Then, this releases a dye, which will cause a line to appear on the test strip. 

If the control line and the test line appear, then the test is yielding positive results and the woman is pregnant. Should the control line appear, and the test line doesn’t, then the test worked – but the woman is not pregnant.

If the “control” line does not appear, then the pregnancy test was inconclusive. When this occurs, we recommend visiting a gynecologist for a blood, pelvic or sonogram test. In the event of questionable results, it’s possible your pregnancy test is showing a false negative or positive; we recommend trying another test for a more reliable outcome.


Conclusion – Stony Brook Women’s Health

At Stony Brook Women’s Health, we’re passionate about helping all of our patients make the best choice for them. We supply urine pregnancy tests to all of our patients free of cost.

Our experienced and caring staff will educate all patients about their potential options, and enable them to take the appropriate step they feel is right.