OPKs and fertility medication

The ovulation predictor kit (OPK) can be a handy tool for women who are trying to conceive. But women who are getting treated for infertility should regard their OPKs with a grain of salt. As helpful as OPKs can be, there are some cases where they should be used in specific ways. Knowing the nuances of fertility medication and OPKs helps you avoid those annoying and often emotionally draining false positives.

How OPKs work

OPKs don’t test for ovulation; instead, they measure the amount of luteinizing hormone (LH) in a woman’s body. LH levels increase in the 36 hours before ovulation, so when LH is high, the woman is close to ovulation. Common OPKs include those made by Clearblue and e.p.t.

OPKs and fertility treatment

Things get a little more complicated when there are certain fertility drugs in someone’s system. Women who are receiving hormone treatment often have to wait a few days before they use an OPK, to allow the hormones from treatment to leave their system. Otherwise, the test may show residual LH from the hormone treatment – not from their body’s actual ovulation cycle.

OPKs and Clomid

Clomid (clomiphene citrate) stimulates the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which helps women ovulate. Most women start taking Clomid around cycle day 5, take Clomid for five consecutive days, and then start ovulating between five to nine days later.

If a woman takes an ovulation test too soon after taking Clomid, though, the OPK might detect the LH from the treatment and interpret it as her body’s natural LH. To prevent this, women who are taking Clomid for fertility should wait at least three days after taking Clomid before using an OPK. For example, if you take Clomid on cycle days 5 to 9, you should test for ovulation on day 12.

OPKs and gonadotropins

Gonadotropins are a second option for fertility medication. Gonadotropins are slightly more expensive than Clomid, carry more risks of side effects, and have a higher risk of a multiple pregnancy, but they can help women who don’t respond to Clomid. They’re similar to Clomid in that they involve the hormones LH and FSH, but instead of prescribing the medication orally, the doctor will perform an injection of LH and FSH.

Because these treatments influence LH levels, they can affect OPK results, so it’s best to wait three days after treatment before using an OPK.

An exception: OPKs and Metformin

Metformin helps many women who are infertile, including women with PCOS, begin experiencing regular menstrual periods and ovulation cycles. Metformin helps the liver know when to stop glucose production, which lowers blood sugar levels. Metformin is the exception to treatments that could interfere with OPKs: because it doesn’t affect LH levels, it generally doesn’t affect OPK results.

The bottom line

Women who are taking medications for fertility should always be aware of how those medications can affect other aspects of TTC. If you are unsure, ask your provider to explain the effects of medications that you’re taking. Usually, waiting three days after treatment is enough to give a woman a clear answer, but in some cases, other steps are needed.

  • Mayo Clinic Staff. “Intrauterine insemination (IUI).” MayoClinic. Mayo Foundation for Medical Education and Research, Jun 21 2016. Web.
  • “What is Clomid and how does it work?” AIWHC. Associates in Women’s Health Care, 2011. Web.
  • “New information on how Metformin works.” Report on article published in Cell, May 2009. DiabetesinControl. DiabetesinControl.com, 2016. Web.
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