A blood test can confirm whether you have ovulated. The hormone progesterone rises in the second half of your cycle, about 7 days after ovulation. In a 28-day cycle you therefore test around day 21. A value above a certain level fits with an ovulation that has taken place.
Many women use ovulation tests from the chemist, which measure the LH surge. My take: those tests predict ovulation, but do not confirm that it actually happened. Progesterone in your blood does. Below you read how that works, when to test and what the result means.
How do you confirm ovulation with a blood test?
After ovulation the empty follicle turns into the corpus luteum, which makes progesterone. That rise is the proof that ovulation took place. A single measurement at the right moment shows it (NHG, Thuisarts.nl).
A urine ovulation test measures something else: the LH surge that triggers ovulation. That surge comes before ovulation, so a positive test means your body is getting ready, not that it succeeded. That is why progesterone is the value that confirms afterwards.
When do you test progesterone?
The best moment is about 7 days after your likely ovulation, or 7 days before your expected period. In a 28-day cycle that is around day 21. With a longer or shorter cycle that moment shifts. The table below helps you pick the right day.
| Length of your cycle | Estimated day of ovulation | Best day to test progesterone |
|---|---|---|
| 24 days | around day 10 | around day 17 |
| 28 days | around day 14 | around day 21 |
| 32 days | around day 18 | around day 25 |
| Irregular or unknown | variable | 7 days before your expected period |
Count day 1 as the first day of your period. If you have an erratic cycle, a fixed test day is tricky. In that case a repeated measurement or a series of progesterone values can give a more reliable picture than a single draw (Leiva et al., 2023). Want to understand your cycle better first? Read our article on your menstrual cycle and hormones.
Progesterone or an LH test: what is the difference?
Both hormones belong to ovulation, but they tell you different things. LH rises just before ovulation and helps you time when you are fertile. Progesterone rises after and confirms whether ovulation actually happened.
For planning intercourse an LH test is handy, because it announces your fertile days. For the question "did I ovulate?" progesterone is the logical choice. In practice they complement each other: LH beforehand, progesterone afterwards.
What does a low progesterone value mean?
A low progesterone value at the expected moment can mean there was no ovulation, or that you tested on the wrong day. The latter happens more often than you think, especially with an irregular cycle. So a low value is not a diagnosis.
Sometimes it points to a cycle without ovulation, which can happen to any woman now and then. If ovulation fails more often, a doctor can look into possible causes, such as PCOS or a thyroid problem. So always discuss an abnormal result with your GP.
Confirming ovulation through Lunara
You can have a progesterone measurement done without a referral. The Ovulation Confirmation is made for exactly this: you test at the right moment in your cycle and see whether your progesterone fits with ovulation. You receive your result digitally, with context from a BIG-registered doctor.
Want to look wider than just ovulation? In the overview of fertility testing you read which other hormones belong to it. And if you are unsure which test fits a wish to conceive, see which blood test when trying to conceive.
Frequently asked questions
Can I ovulate without noticing?
Yes. Not everyone feels ovulation. Some women notice mild belly pain or changes in mucus, others nothing. A progesterone measurement shows whether ovulation happened regardless of what you feel.
Do I ovulate every cycle?
Not always. A single cycle without ovulation happens to many women and is usually no problem. If it keeps happening, it can be worth having your hormones looked at and discussing this with a doctor.
References
- Leiva R, et al. Serial progesterone levels more accurately predict the time of ovulation in subfertile women: a prospective cohort study. J Assist Reprod Genet. 2023. PMID: 37351803.
- Practice Committee of the American Society for Reproductive Medicine. Optimizing natural fertility: a committee opinion. ASRM, 2022.
- NHG and Thuisarts.nl. It is not working to get pregnant (subfertility). Dutch College of General Practitioners. Available via thuisarts.nl.
Every blood test result through Lunara includes a professional assessment by a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
Author
