Am on progesterone suppository.is there any way to find placenta has taken over progesterone production at 12 wks before stopping suppository?

Take over: This question is important and I strongly suggest you discuss this with a gynecologist.

Luteal phase defect: I use progesterone in the 1st trimester quite a bit for borderline progesterones and luteal phase defect. I don't check the levels after 12 weeks because the placenta produces a sufficient amount and losses from low progesterone occur much earlier. Certainly a progesterone can be done once off the suppositories, but while you're taking them the level in your blood will reflect total progesteron