How and when to use pregnancy tests

When you are trying to get pregnant and would like it to happen fast, it can be agony to wait and see if your period is coming or not. Home pregnancy tests are easily available and relatively inexpensive, and the most sensitive tests can detect pregnancy up to several days before your expected period.

How pregnancy tests work

Home pregnancy tests work by detecting the presence of the hormone hCG (human chorionic gonadotropin) in your urine. The production of hCG starts when the fertilized egg (the embryo) implants in your uterus around six to twelve days after ovulation (read more about this our article about conception).

Your first morning urine is usually the most concentrated urine of the day, and is therefore most likely to have a detectable amount of hCG in it.

If you are testing early (before 14 days after ovulation), using your first morning urine will usually give the most reliable result.

How early can I test?

During the first couple of days of your pregnancy the level of hCG in your urine is still too low to be detected, but it doubles approximately every two days.

How and when to use a pregnancy testhCG levels are expressed in mIU/ml or “milli-international units per milliliter”, often just as mIU.

The most sensitive tests can detect as little as 5 mIU/ml, and these may show a positive result as early as 8 days past ovulation (“DPO”).

It is possible to get a positive test even earlier, but it’s not common, and many pregnant women will not get a positive test until 10, 12 or even 14 days after ovulation.

Early testing can be very exciting, but also rather nerve-wrecking. If you can stand waiting until 12-14 days past ovulation, you can feel reasonably confident that the test result is accurate.

How to interpret pregnancy test results

Digital pregnancy tests

Digital pregnancy tests leave no room for interpretation. They have a window where the test result is spelled out in words – “Pregnant” or “Not pregnant”.

Do not try to disassemble a digital test to look at the test lines inside it, as there may be two lines even if you are not pregnant. Trust the results window, or try again a couple of days later if you think you may have tested too early.

Midstream and strip tests

Traditional tests have two antibody strips on them, either two parallel lines or two lines shaping a plus sign (+).

One of the strips will always turn pink or blue (depending on the brand), whether you are pregnant or not. This is the control line, which is just there to confirm that the test is working.


The other strip, the test line, will turn pink or blue only if it’s exposed to urine containing hCG.

Positive pregnancy test

Photo by Esparta / CC BY

If you’re not pregnant, or if you are testing too early to detect any hCG in your urine yet, the test will show a negative result: only the control line is visible. If you are pregnant, the positive result will show as two parallel lines or a plus sign.

If you’re testing early (before 12 days past ovulation), the test line may be very faint. That doesn’t matter: If the line is there, you’re pregnant!

Keep in mind, however:

  • The test result is only valid during the first 10 minutes after testing. It’s not uncommon for pregnancy tests to develop a faint test line after some time. Such lines do NOT mean you are pregnant. Read the result within 10 minutes after testing, then discard the test.
  • On many tests, the antibody strip can be seen as a gray or colorless line, which may appear at any time after testing. Such “ghost lines” or “evaporation lines” must not be mistaken for a positive result: The test must have a pink or blue test line in order to be interpreted as positive.

Happy testing!