Another cause may be the mother not having enough progesterone. If a woman is diagnosed with low progesterone levels in the second half of her menstrual cycle (the luteal phase), she may be prescribed progesterone, to take during the first trimester of her pregnancy. However, when a woman might already be miscarrying, there is no evidence that first-trimester progesterone pills decrease the risk of having a miscarriage. Scientists have even questioned whether problems with the luteal phase really can cause miscarriages.