How to read an ovulation test (LH strip)

Ovulation predictor kits (OPKs) are one of the most popular ways to time sex when trying to conceive — and one of the most confusing to read. Unlike pregnancy tests, a visible test line on an ovulation test doesn’t necessarily mean “positive”. Here’s how they work.

What ovulation tests detect

OPKs detect luteinising hormone (LH) in urine. LH is always present at some level, then rises sharply in the middle of the cycle. This LH surge triggers ovulation; the FDA says it usually happens about one to one and a half days before ovulation. Some kits also measure an oestrogen-related hormone to widen the window they detect.

How to read the lines

Because LH is usually present, a faint test line is normal for much of your cycle. What matters is how the test line compares with the control line:

• Test line lighter than the control: negative — no surge detected yet.
• Test line as dark as or darker than the control: positive for most brands — an LH surge.

Always check your brand’s instructions, as some kits read differently. Digital tests show a symbol instead of lines.

When and how to test

1. Start at the right point in your cycle. Your test’s instructions use your usual cycle length to suggest a start day. Starting too late can miss the surge.
2. Test at a consistent time each day. Many brands suggest avoiding first-morning urine; follow yours.
3. Limit fluids beforehand. Dilute urine can make the test line look lighter.
4. Consider testing twice a day near your expected surge. Some surges are short enough to fall between daily tests.
5. Read within the reading time, then record the result.

Reading a pattern, not a single strip

Judging line darkness by eye across days is difficult. Comparing the ratio of the test line to the control line on each strip makes it easier to see a surge build and fall. That’s the approach LineCheck’s ovulation test scanner takes, placing each strip on a Low, Rising, High or Peak stage and charting them across your cycle.

The limits of ovulation tests

• They don’t confirm ovulation. A surge usually leads to ovulation, but not always. A sustained rise in basal body temperature afterwards, or a blood test arranged by a doctor, can help confirm it.
• Some conditions affect results. Polycystic ovary syndrome (PCOS), approaching menopause and some fertility medicines can cause raised LH or misleading results.
• They’re not contraception. The FDA notes ovulation tests aren’t reliable for preventing pregnancy.

If you’ve been trying to conceive for a year (or six months if you’re 35 or older), or your cycles are very irregular, it’s worth talking to a doctor.