You might find ovulation predictor kits (OPKs) listed under the definition of a love/hate relationship. They're easy to use and helpful to determine the fertile window but frustrating for many women. Here are 7 reasons why using OPKs can be misleading, and what you can do to confidently determine your fertile window.

1. They don’t guarantee ovulation 

A surge in LH (luteinizing hormone) is the trigger for ovulation, and this is the hormone that OPKs test for. But that's it. It's possible to have a cycle where ovulation does not occur (the egg is not released from the ovary) even though LH levels rose appropriately. (This is called LUFS for luteinized unruptured follicle syndrome).

2. They might not catch your LH surge 

 Some women have LH surges that naturally peak below the threshold that the kit detects. Others may have an LH surge that lasts shorter than 10 hours, and if they test once daily, they might miss it. For women with irregular cycles, the 5 to 9 strips in the kit might not cover the range of days needed to test, since it is more difficult to predict when to start testing. Not testing at the right time of the month is the biggest problem with OPK's that I see in practice. 

3. They don’t differentiate between a true and a false surge 

A true surge should only be detected on one day. If it shows on more than one day, chances are the result is false. An example of a false surge is where there are has multiple mini peaks of LH before the real surge. This is more common with women who have PCOS, and results in timing intercourse too early – sperm don't survive long enough for the release of the egg. Another example is the natural rise in LH not connected to ovulation when we get closer to menopause.

4. They don’t account for Short Luteal Phases 

OPK's instruct to test based on an average length luteal phase. The luteal phase is the second half of the cycle from ovulation to menses, usually lasting 12 -16 days. Women with luteal phases less than 10 days are actually testing too early, and would be led to think they didn't ovulate at all when they're ovulation is still coming up!

5. They don’t test for fertile signs 

Cervical fluid changes throughout the cycle, and creates tracks for sperm to travel up to the egg when in a fertile state. OPKs don't account for these signs and don't always line up with fertile signs. This is particularly important when timing a non- medicated IUI 

6. Results can be affected by drugs 

Most fertility drugs, antibiotics like tetracycline, hormone therapy, postpartum and breastfeeding can affect the results.

7. They are not pregnancy tests

If you happen to already be pregnant, the kit will show that you aren’t ovulating but does not indicate that it is because you are pregnant.  

So how to avoid these potential pitfalls? Charting! Tracking your cervical fluid changes, other fertile signs and basal body temperature is the best way to determine whether ovulation is actually occurring, the length of the luteal phase, if you have conceived, and when to time intimacy compared to using OPKs alone. (Get the run down on how to chart your cycles here).

OPKs are super useful, but only help when they’re used at the right time, which charting can help determine.Tips for turning an OPK: test twice a day, avoiding the first morning urine. Try to avoid fluids for two hours before checking for urine to be more concentrated. 

Interested in boosting fertility? Get your guide on the three best nutrients to enhance egg health here.