So you just started tracking your cycle, but have a million questions about how ovulation tests will work with your specific situation? Wondering if OPKs will work if you’re pregnant already? If you’re on BC? If you have PCOS? OBGYN Dr. Mare explains various scenarios and whether OPKs will accurately help you track your cycle.


By Dr. Mare Mbaye

Anyone who is trying to conceive has heard a little something about ovulation predictor kits (commonly known as OPKs). These kits are widely available now through many retailers (including yours truly) and are generally over 95% effective when used correctly. But while OPKs can be a great addition to one’s arsenal on his/her TTC journey, there are some pitfalls to be aware of.

What do OPKs even test for?

Let’s start with the first pitfall—OPKs do not actually test for ovulation. They work by detecting a surge in the body’s production of luteinizing hormone (LH). This occurs anywhere from 16-48 hours before ovulation. Most OPKs can detect the surge between 18-24 hours prior to ovulation. They therefore can’t actually confirm whether or not ovulation follows—hence the name ovulation predictor kit. For most people, however, timing intercourse shortly after this LH surge is confirmed will increase the odds of fertilization since this is the window during which conception is most likely to occur

Another pitfall is that while OPKs are useful, they are better in conjunction with other testing, such as assessment of cervical mucus and basal body temperature. OPKs are urine-only tests and therefore won’t tell you if your cervical mucus is conducive to fertilization.

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So, when are OPKs less effective?

Here is a list of the most common scenarios:  

  • Will ovulation tests work if you’re pregnant? Ovulation tests can (sort of) act as a pregnancy test because LH is molecularly very similar to hCG. If you are pregnant, your hCG levels will be much higher than normal and an OPK may inaccurately detect this and read it as a high LH value. This is not to say that OPKs can substitute for a pregnancy test—pregnancy tests are much more accurate.
  • Will ovulation tests work if you’ve had a recent pregnancy loss? If you have a pregnancy loss, your hCG levels will be much higher than normal and an OPK may inaccurately detect this and read it as a high LH value.
  • Will ovulation tests work if you’re taking fertility drugs? For the same reason as in the cases of pregnancy and pregnancy loss, OPKs do not function reliably when injectable fertility drugs such as Pergonal or Profasi (the hormone hCG) are present in the system.
  • Will ovulation tests work for women over 40? For some women in their 40s, especially those nearing menopause, LH levels may be increased to a high enough point that they render the tests invalid.
  • Will ovulation tests work if you have a failed egg release? Occasionally, an egg fails to emerge from its follicle after the LH surge has occurred. This condition is known as luteinized unruptured follicle syndrome (LUFS) and is more common in those with infertility.
  • Will ovulation tests work if you have irregular periods? This is not a hard and fast “no,” however irregular periods point to an underlying issue with hormonal balance that will often render OPKs unreliable. Per the ASRM, those with periods that are not consistently 25-35 days should therefore not use them.
  • Will ovulation tests work for people with PCOS? People with PCOS can have a baseline high level of LH or several LH surges throughout their cycles that make OPKs unreliable for them as well. Even people without PCOS can at times have small LH surges before their full peak that can lead to false positives before the appropriate time. 
  • Will ovulation tests work if you are on birth control? Because most forms of contraception suppress ovulation, OPKs cannot be used reliably while someone is on them.

These are the biggest contributors to false results when using OPKs. If any of these describe you, it may be worth talking to your doctor about what other methods you can use in conjunction with or instead of OPKs.

Other common conditions

You’ll notice I didn’t mention endometriosis in the list above and for good reason.

  • Will ovulation tests work if you have endometriosis? Patients with endometriosis still ovulate normally, so OPKs should work just as well for them. The major issue with these patients is related to internal scarring and inflammation, especially of the fallopian tubes, which affects the ability of the sperm and egg to meet.

Other methods

It’s important to remember that while OPKs are an easy and effective way to predict ovulation, they are not the only option, and they aren’t foolproof. Using them with cervical mucus and basal body temperature assessments will improve your ability to predict your exact fertile window. As a result, while it’s good to focus on the fertile window, it won’t hurt to have regular intercourse before you get that positive OPK result.

Shop ovulation predictor kits (OPKs) here.