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Progesterone - When & Why

Number 7 of 12 posts in 12 days discussing 12 different things to investigate when trying to explain unexplained infertility . . .



This seems such an obvious one, but is often tested poorly. Too many GPs instruct women to test progesterone on day 21 without pausing to try to work out whether day 21 is the right day to test.

Progesterone isn't meant to be tested on day 21.

Progesterone is meant to be tested 6-7 days after ovulation!


There are statistics out there suggesting that only 13% of women actually ovulate on day 14. So that means only 13% of women should be testing progesterone on day 2, and 87% of women testing progesterone on day 21 are testing it too early or too late. If you take it at the wrong time, the information is difficult to interpret correctly and can cause unnecessary worry. If a GP doesn't understand this, they will simply insist on testing progesterone on 'day 21', some people work out when it will be 6-7 days after they ovulate, and tell the GP that is day 21.


Progesterone is important - it is the hormone that enables your body to delay a menstrual bleed for long enough to allow an embryo to implant. If there isn't enough progesterone, it is likely your luteal phase will be short and if so, any attempted implantation would be likely to be swept away with the period.

What do the results mean?

  • 30 nmol/L or over shows that you have ovulated

  • 15-30 nmol/L suggests that you have probably ovulated, but that the test may have been taken too early or too late in the cycle. If this is you, look at how many days were there between your test and the start of your bleed. Your bleed should have started 6-7 days after you took the test if you timed the test correctly.

  • 15 nmol/L or less shows that you have not ovulated

If progesterone is low, the simple response is to supplement with progesterone - but that is a very Western med way of looking at health. Yes, it answers the problem of there not being sufficient progesterone - but it doesn't address the issues of why, or do anything to support the body to build better follicles or to produce more progesterone. In my opinion it would be better to see if you can figure out why progesterone is low and fix it. Low progesterone could be an indicator of poor follicle structure, insulin resistance can lower progesterone receptivity, thyroid issues can play a role in low progesterone, low iron can play a role, poor circulation in and around the ovaries can play a role - getting to the root cause can be really helpful for overall fertility rather than just opting for progesterone supplementation. If progesterone is low because there are issues impacting follicle development, taking supplementary progesterone may improve the cycle timing, but won't improve egg quality or fertility. If you can figure out why progesterone is low, you can usually improve it - which in turn will indicate improved follicles and improved fertility. And if you are able to do that, it will do more for your fertility than simply taking progesterone so you can hit a blood test marker.


In my clinic, this isn't in my list of initial tests for a client to do. I rarely have enough detail about their cycle at the beginning to know for sure when they should test progesterone. I also find that if we test it at the beginning of our time working together, it is often low and people really worry about that. It can take 2-3 months to see a significant rise in progesterone, and that is quite a long time for someone to be worried. If possible, I hold off until I am pretty confident about when they ovulate and I have had enough time to improve the level of progesterone before requesting they run a progesterone test.

I'm a @FertilitySupport Trained Acupuncturist, we understand what is going on, so we can help you to understand

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