21 Progesterone Test

Dear doctor. . .

A couple weeks ago, I sought the help of a doctor because last cycle I began very light spotting 5 days after I ovulated. I expressed concern to my doctor that I've been trying to conceive unsuccessfully for a few months, and she decided to do an FSH test and a 21 progesterone test. (The FSH test came out normal) She explained to me that the 21 progesterone test had to be done on day 21 of my cycle.  I explained to her in detail that my cycles are around 36-37 days long, and I typically don't ovulate until cd 24 or 25.  (I have confirmed ovulation by using OPKs and BBT)  She still had me get the 21 progesterone test done.

So, today I get a letter in the mail from my doc telling me that on CD 21 my progesterone was low.  The levels on that day were .3 ng/ml.  Well, of course they would be low.  This cycle I didn't ovulate until CD 25.

My question(s) is this: why does the progesterone test need to be done on CD 21 even though the doc knows I ovulate later?  And how do I determine if low progesterone is the reason I started spotting only 5 days post ovulation last cycle?

Any insight would be appreciated?  I fully expected my progesterone levels to be low on cd 21, but I want to find out the reason for the spotting, and if in fact I have low progesterone post ovulation as well.  (I've heard spotting is a main sign of low progesterone)

[John Kim, M.D.]

I agree with you. The peak progesterone level should be 7 days after ovulation or 7 days after your ovulation kit is positive not arbitrarily CD21.