Quick answer: A day 21 progesterone test checks whether you ovulated in that cycle. A level above about 3 ng/mL (10 nmol/L) usually means you did, and above about 10 ng/mL (30 nmol/L) is a good result. A low result most often means the test was done on the wrong day, so check the timing before worrying.
The timing matters more than "day 21"
Progesterone peaks about 7 days after ovulation, which is about 7 days before your next period. "Day 21" only works for a 28-day cycle:
| Your usual cycle | Best day for the test |
|---|---|
| 28 days | Day 21 |
| 30 days | Day 23 |
| 32 days | Day 25 |
| 35 days | Day 28 |
Day 1 is the first day of full bleeding. If your cycle is irregular, the doctor may repeat the test weekly or suggest follicular tracking scans instead.
Reading your result
- Below 3 ng/mL (10 nmol/L): ovulation probably didn't happen, or the test was too early or too late.
- 3 to 10 ng/mL (10 to 30 nmol/L): ovulation likely happened.
- Above 10 ng/mL (30 nmol/L): good evidence of ovulation.
Labs report in either ng/mL or nmol/L (1 ng/mL is about 3.2 nmol/L), so check the units on your report.
Why might I not be ovulating?
- PCOS, the most common cause
- Thyroid problems or a high prolactin level
- Being very underweight or overweight, intense exercise or major stress
- Approaching menopause
One low result isn't a diagnosis. Many women have the occasional cycle without ovulation.
What next?
If the result is low and the timing was right, our doctor may check thyroid, prolactin, LH, FSH and AMH, and arrange a scan. See fertility tests for women for the full picture.
Get tested in Akoka
The progesterone test is walk-in at Mascot Healthcare, 52 Sholanke Street, off Chemist Junction, Akoka, Lagos, Monday to Saturday, 9 AM to 5 PM. No fasting needed. Prices are on our price list.
This article is general information, not a diagnosis.