discontinuing prometrium in early pregnancy?

I have pcos and my doctor has me on 400 mg of prometrium (progesterone) on cycle days 17 through 26. My question is - if I were to get pregnant, would going off the progesterone at the end of the 10 days cause me to miscarry the baby? Now, I know, I know, ask my doctor. I will at my appointment next month, I just want to know earlier without bugging my nurse AGAIN, haha. My doctor has ok'd my husband and me to begin clomid, so I will be having an ultrasound to make sure I don't have any cysts before we do the cycle of clomid and an hsg test; this is when I plan to ask. I've forgotten to ask at my last 2 appointments, and I'm just very curious to know at this point. Thanks :)

some extra facts:

I'm 21, have been trying to get pregnant for 11 months, and have had one very early miscarriage (I was on prometrium when bleeding started).