Maternal infection with a large number of different organisms has been associated with an increased risk of miscarriage. Some very early signs of miscarriage are often bleeding that looks like a heavy period.
Up to 25 percent of all pregnant women have bleeding at some point in pregnancy, about half of those will have a miscarriage. Bleeding that is a sign of miscarriage may be scant or heavy. It may be constant, or it may come and go. Bleeding may be followed by cramping abdominal pain and, in some women, lower backache.
No study has shown that general first-trimester progesterone supplements reduce the risk of threatened miscarriage (when a mother might already be losing her baby), and even the identification of problems with the luteal phase as contributing to miscarriage has been questioned.