After you ovulate, the corpus luteum -- the leftover shell of the ovulated egg -- produces progesterone. Progesterone helps prepare the uterine lining so that a fertilized egg can implant and grow. Low progesterone won't prevent ovulation or fertilization of the egg, but it could prevent the uterine lining from adequately supporting a fertilized egg, obstetrician Dr. Joseph Krotec explains. This can lead to an early miscarriage. You might not realize you were pregnant if a miscarriage occurs so early that you bleed near the expected time of your period. Supplemental progesterone can improve the uterine lining.