So many women we see don’t do a progesterone test on the right day and wonder why it comes back low. This leads them to think that they are not ovulating, but the timing of the test is really important. The main test to check whether a woman is ovulating is by a blood test to check the level of the hormone progesterone which increases following ovulation.
Women are generally told to do the test about one week before their next period is due. As the ‘average’ cycle is 28 days long (counting from day one of your period up until the day before your next period starts) – this means that the best time for a progesterone test in a 28 day cycle would be Day 21. This is why the test is often called the ‘Day 21’ progesterone test.
The difficulty with this approach is that women’s cycles are not always 28 days long and can vary from one cycle to the next. Counting back days before the next period often results in the test being mis-timed.
Timing of Progesterone Tests
Ovulation normally occurs about 14 days before the next period, and the time before ovulation can be much more varied. To improve the accuracy of progesterone tests, aim for the test to be done approximately 7 days after ovulation – this is mid-way between ovulation and the next period (mid-luteal phase), when the progesterone should be at the higher level.
As ovulation is a ‘hidden event’ in women, this can make the timing of the test more difficult. There are three ways to get prospective information to help with the timing of the test:
- 7 days after the LH surge as shown by an ovulation prediction kit (urine test kit such as ClearBlue ovulation predictor kit, or 7 days after the ‘O’ symbol on Persona)
- 6 days after your waking temperature goes up to the higher level (if properly taken)
- 7 days after peak day (peak day is the last day of wetter, clear, slippery secretions)
Your test results are normally interpreted after your next period date is known to ensure that the test has been appropriately timed. If your period starts about a week after the test, it was likely to have been well-timed. The most common reason for a poor test result is a mis-timed test.
What to look out for:
- A progesterone level above 30 nmol/l is considered proof of ovulation (in that cycle)
- A level between16-30nmol/l is usually repeated in another cycle. This indicates a strong possibility of ovulation, but possibly a mistimed test
- A result of less than 16 nmol/l indicates that the test should be repeated in another cycle
- A consistently low result usually indicates the need for referral to a specialist