Your doctor may have suggested that you have a progesterone test to confirm ovulation or to assess your progesterone levels in the luteal phase. Or you may have recently had a test and are dumbfounded to be told that you’re not ovulating. The secret is all in the timing!

The main test to determine whether a woman is ovulating is by a blood test, which assesses the level of the hormone progesterone. Progesterone increases in the bloodstream following ovulation and reaches its peak at 7 days before the next menstrual period. This test is termed a 21-day progesterone test and is performed on day 21 of a 28-day cycle.

However, the majority of women don’t have regular 28-day cycles and this can cause confusion on when best to test and worst still, inaccurate test timing leading to a woman being told that she’s not ovulating. Incorrect timing of progesterone testing is common and to get the best result, it’s important to be as accurate as possible in timing the test.

Regular cycles

If you have a regular cycle and you know when you have ovulated, it is reasonable to organise your progesterone test for 7 days post ovulation. You can accurately determine ovulation by observing your natural fertility indicators – your body temperature and cervical mucus.

Irregular cycles

If you have lengthy irregular cycles, timing your progesterone test is a little more complex. Whilst the time to ovulation can vary, the time from ovulation to your next period is always consistent. After ovulation, your next period will occur 10-16 days later. It is recommended for lengthy irregular cycles that the initial test is performed later (for example day 28 of a 35-day cycle) and then repeated weekly until the next menstrual period starts (NICE Guidelines April 2018). A useful check to determine whether the timing of your test was correct is if your next menstrual period occurs around 7 days following your test.

Progesterone test results

When considering your result, it’s important to remember that the most common reason for an inadequate result is poor timing. If you think this might be the case, ask your doctor for a repeat test next cycle.

• A progesterone level of 30nmol/l or above is indicative of ovulation in that cycle
• A result between 16-30nmol/l indicates that ovulation is likely to have occurred, however may have been mis-timed and a repeat in the next cycle is recommended.
• A level that is less than 16nmol/l may mean that ovulation has not occurred and the test should be repeated in the next cycle.
• A consistently low result over subsequent cycles may show lack of ovulation and possible progesterone deficiencies. Ask your doctor for a referral to a specialist to discuss what this may mean for you and possible treatment.

Reference:
NICE (2018) Assessing and managing ovulation disorders https://pathways.nice.org.uk/…/assessing-and-managing-ovulation-disorders.pdf (Accessed 12/06/18)

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