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Pregnancy tests and ovulation predictors: How do they work?

Whether you're pregnant or you're trying to conceive, understanding how ovulation predictors and pregnancy tests work can help you know where you are early on in your pregnancy journey. Let's talk about both of them now. 

Ovulation predictors: How do they get the timing right?

If you're trying to get pregnant, you may want to use an ovulation predictor. Knowing when your body will release a new egg, or ovulate, will help you and your partner time sex around the most fertile part of your cycle. 

Here's how they work: Ovulation predictors look for a substance called luteinizing hormone (LH) in your urine. Your pituitary gland regularly pumps out a small amount of LH. A surge in LH happens right before you ovulate. This prompts your ovaries to release an egg.

Some ovulation predictor kits also measure another hormone called estrone-3-glucuronide (E3G). E3G is made when estrogen breaks down in your body. It builds up in your urine right around ovulation. E3G causes your cervical mucus to become thin and slippery. This is thought to help sperm swim more easily and make it easier to become pregnant.

Different ovulation predictor kits work in different ways. You might add a few drops of your urine to the test, hold the tip of the test in your urine stream while you're going to the bathroom, or dip the test in a cup of your urine. You should get the results of the test in about 5 minutes.

Most kits come with multiple tests so you can check your urine over several days to find your most fertile time. Follow your kit's instructions carefully for the most accurate results. 

A positive result usually means you should be ovulating in the next 24 to 36 hours.

Oh, and here's a caution: You should only use this test if you're trying to become pregnant—not if you're trying to avoid pregnancy. This isn't a reliable test for that purpose.

Home pregnancy tests: What should you do for accurate results?

A home pregnancy test also measures a hormone in your urine. This time it's human chorionic gonadotropin (hCG). HCG is made by your placenta shortly after a fertilized egg—or embryo—attaches to the wall of your uterus. In other words, your body only produces this hormone if you're really pregnant.

Different home pregnancy tests work in different ways. You might hold a test strip in your urine stream or dip a test strip in a cup of urine. If you're pregnant, most test strips produce a colored line, but this will depend on the brand you're using.

For the most accurate results:

  • Test one to two weeks after you've missed your period. That should be enough time for hCG to show up in your urine.
  • Test your first morning urine. It's likely to have more hCG in it than urine later in the day.

If your results are positive, call your provider's office for an appointment. He or she can confirm your pregnancy and you can begin prenatal care. 

If your results are negative, you still might be pregnant. Try another test in a few days. (If you're pregnant, your hCG levels should double every 48 hours.) If your results are still negative but you think you're pregnant, call your provider.

Already know you're pregnant?

Discover how your provider dates your pregnancy. Hint: it's not based around the date of conception. 

Sources: National Institutes of Health; Office on Women's Health; U.S. Food and Drug Administration

Reviewed 12/6/2023

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