If you’re trying to get pregnant, you’ve probably experienced the agony of wondering when to take a pregnancy test. Especially when you’re experiencing potential early signs of pregnancy like nausea, headaches, and fatigue, it can be hard to resist testing early. Do you really need to wait until the first day of your missed period, or can you test earlier?
There are really two answers to this question: when you can, and when you should.
Nothing is stopping you from taking a pregnancy test any time you want. But if you take it before 8 days past ovulation (DPO), you’re probably wasting your money and setting yourself up for unnecessary disappointment.
The reason why has to do with when implantation occurs. Even if conception has occurred, the fertilized egg does not start producing hCG—the hormone that pregnancy tests detect—until after implantation is complete. (And speaking of implantation … read our post on the truth about implantation bleeding.)
While it’s technically possible for implantation to occur any time between six and 12 days after ovulation, 85 percent of the time it occurs between eight – 10 DPO, and it only occurs at 6DPO 0.5% of the time1.
After implantation, hCG levels start doubling roughly every 48 hours. Baseline hCG levels, early pregnancy hCG levels, and hCG doubling time vary from woman to woman and from pregnancy to pregnancy. Along with the date of implantation, these factors will influence how early you can get a positive pregnancy test.
Deciding when to take a pregnancy test is a risk-benefit calculation: testing earlier than 12 DPO means weighing the risk of being disappointed about a possibly false result against the unlikely outcome of an early positive.
How to avoid a false positive pregnancy test
- Do not test earlier than 12 – 14 days after ovulation.
- Repeat the test two days later, regardless of the results. If you get a negative result the first time, it may be because your hCG hasn’t risen enough yet for the test to detect it. If you get a positive result, a second test two days later can rule out a very early pregnancy loss, also known as chemical pregnancy.
- Make sure to use a high quality pregnancy test known for delivering clear results (learn more about the best pregnancy tests).
What causes a false positive pregnancy test?
- Your LH Peak. Sometimes, hCG can be released from the pituitary at the time of your LH-peak. If you take a pregnancy test during this time, there’s a small chance of a false positive.
- Chemical pregnancy. A high proportion of early pregnancies are miscarried even before the day of your period. Taking a test too early could detect a very early pregnancy that is not viable. Technically, this is not a false positive, because you really were pregnant.
- Perimenopause. Perimenopausal women have somewhat elevated levels of circulating hCG, even when they’re not pregnant. This could lead to a false positive result.
- Infertility treatment. Women undergoing hCG treatment (A.P.L, Pregnyl, Profasi, Pergonal) to stimulate ovulation may also receive false positive results if they test within 10 days of their last injection.
What causes a false negative pregnancy test?
- Testing too early. In very early pregnancy, not all women produce enough hCG for the test to pick up.
- Using a test that is not sensitive enough. If you are testing early, you need to use a more sensitive test.
- Diluted urine. If you drink a large amount of liquid shortly before testing, your urine volume may increase so much that hCG is too dilute to measure.
- Not testing urine immediately. If the urine collected has been sitting around for too long before testing—usually 30 minutes or more—a false negative result can occur.
What type of pregnancy test is best?
If you’re testing on the first day of a missed period, it doesn’t matter very much which test you use—most currently marketed tests are reliable and will yield a positive result for 98 percent of pregnant women. But if you’re testing early, you should use a more sensitive test—just remember that pregnancy tests are less likely to be accurate when taken before your missed period.
The more sensitive the pregnancy test, the more likely it is to detect pregnancy early. But more sensitive pregnancy tests are also more likely to return false positives.
In a study2 that tested six over-the-counter pregnancy tests, First Response and Answer were the most sensitive. Clear Blue Easy and Walmart Equate tests were the least sensitive.