It's kind of a chicken and egg thing. Is your progesterone low because you are going to miscarry, or do you miscarry because your progesterone is low? It hasn't really been proven either way, but there is no harm in trying progesterone supplements if you have had more than one miscarriage. Many women have been able to keep pregnancies with progesterone supplements after they have had multiple miscarriages without.
Progesterone supplements can't harm your baby, so if you are concerned about multiple miscarriages, or suspect you might have low progesterone, BEG YOUR DOCTOR FOR PROGESTERONE SUPPLEMENTS! Begging always works for me :).One more thought on progesterone- if you are having trouble getting pregnant, and have short cycles, you may need progesterone supplements to even get pregnant.
If you have any questions feel free to comment or email me.