How Do Pregnancy Tests Work?

Think you might be pregnant? Taking a pregnancy test is your first step to finding out.

Pregnancy tests are a reliable way to confirm whether or not you’re pregnant. They’re easy to use, widely available, and can provide results in just a few minutes.

Understanding how they work and knowing the best time to take one can help you get the most accurate results. Read on to learn more. Or contact our office to schedule a free pregnancy testing appointment in a safe, welcoming space. (Our Marlborough location provides pregnancy testing and ultrasounds. The Clinton location provides other resources, support, and education.)

How Do Pregnancy Tests Work?

Pregnancy tests detect the hormone human chorionic gonadotropin (hCG), which is produced after a fertilized egg implants in the uterus. Implantation typically occurs 6 to 10 days after ovulation, and hCG levels rise rapidly in early pregnancy.

At-home tests use antibodies that react to the presence of hCG in urine. If hCG is detected, the test displays a positive result, often as a line, plus sign, or digital confirmation.

There are also blood tests that can detect hCG earlier and in smaller amounts, but these are usually done in a medical setting and reserved for cases when your pregnancy is at risk for miscarriage.

When Is the Best Time to Take a Pregnancy Test?

The timing of your test plays a significant role in its accuracy. For the most reliable result:

Wait until after your missed period: This is usually about 14 days after ovulation for most women with regular cycles. Testing too early may result in a false-negative if hCG levels are still low.
Test in the morning: First-morning urine is most concentrated, increasing the likelihood of detecting hCG if you’re pregnant.
Follow up if unsure: If your test is negative but your period doesn’t start, test again in a few days or consult your healthcare provider.

Why Timing Matters

HCG levels double every 48 to 72 hours in early pregnancy. Testing too soon, especially before implantation, may lead to an inaccurate result. If you’re unsure when you ovulated or have irregular cycles, waiting a few extra days can improve accuracy.