What do ovulation tests measure?
Ovulation predictor kits (OPKs) detect the surge in luteinising hormone (LH) that occurs 24–36 hours before ovulation. This surge triggers the release of an egg from the ovary, so a positive test means ovulation is imminent.
Timing intercourse in the days around this LH surge gives you the best chance of conception, since sperm can survive in the reproductive tract for up to 5 days but the egg only lives for about 24 hours after release.
How accurate are they?
OPKs are generally quite accurate — around 99% accurate at detecting the LH surge. However, they don't confirm that ovulation actually occurred, and they can be less reliable for women with PCOS (who may have consistently high LH levels).
It's also possible to miss the surge if you test at the wrong time of day, or if your cycle is irregular and you start testing too late. Testing in the early afternoon is often recommended, as LH is usually concentrated in urine at that time.
How to use them effectively
Start testing a few days before you expect to ovulate — typically around day 10 of your cycle if you have a 28-day cycle. For longer or irregular cycles, you may need to start later or test for longer.
Remember that ovulation tests are just one tool. Combining them with cycle tracking apps, basal body temperature charting, and monitoring cervical mucus can give you a more complete picture of your fertile window.
Related condition
Fertility & trying to conceive →References & sources
- 1.Ovulation and fertility — Pregnancy Birth & Baby
- 2.Fertility — Pregnancy Birth & Baby
- 3.Planning for pregnancy — Pregnancy Birth & Baby
This content is general information and not a substitute for individual medical advice. Please consult a GP for your personal situation.
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