There is a condition called luteal phase defect (low progesterone) which has long been suspected to be associated with recurrent miscarriages. Treatment
medication. The problem is, there is no proof that luteal phase defect exists, or that adding progesterone helps.
At any rate, after six miscarriages, if all testing has come back normal, it probably cannot hurt to use progesterone, regardless of any blood progesterone level.