Why cycle day 21??

[Shanti]

I have some blood tests to check my fertility as we're ttc #2 and it's taking some more time like DD did... and my GP has asked me to get these done on cycle day 21.... I forgot to ask why as I just wanted to get out of the doctor surgery and quickly get what I went in to get....

Can someone please tell me why that day?

Thx.

[Joeve]

From what I can gather as I just had mine done a few weeks back is so they can check to see if you have ovulated. Progesterone is an important measure of your cycle by CD 21.

[briggsy's girl]

if you ovulate (theoretically on day 14), a week later, your progesterone levels will be high enough to tell if you've ovulated. if you're having an anovulatory cycle, progesterone would be less than about 30 (from memory), if you have ovulated it will be higher than that

[LionsandBears]

It's based on the assumption of a 28 day cycle, with ovulation occuring at CD14. Based on that assumption, the progesterone levels 7 DPO (days past ovulation) show whether or not you've ovulated. 7DPO is CD21 on this assumption. To women who ovulate later in their cycle, it may be better to time it at 7DPO rather than CD21. It depends on whether or not you know when you ovulate. Otherwise, just go with CD21 and see what it says.

I always had a 12 day luteal phase, so would get the test 6DPO, but that's just me.

[Shanti]

Thanks so much everyone for your help. That's been very helpful. I quite often ovulate around cd15-18 (it varies) so not always on cd14..... I'll take it on cd21 and see how that goes anyway.

[Olive]

i had a bloodtest with DD1 on day 23 because i ovulated at the time around day 18-19, from memory my level was below 30 but i still ovulated (obviouslt )
goodluck darl xxx

[briggsy's girl]

it's only an indicative test. it's often used as a guide - especially if you start taking fertility drugs like clomid - they'll take the test at day 21 (which is crazy, given most O later on clomid anyway) - and if it shows no sign of ovulation, they will start discussing drug changes once AF arrives. if it does show O signs, they'll look at when to do a pg BT