Prometrium, a progesterone supplement, is sometimes prescribed during the first trimester of pregnancy in women who have had a history of miscarriages caused by low progesterone levels. The addition of prometruim during pregnancy helps ensure that the women will carry the fetus to full-term. It works by helping ensure that a placenta is fully formed thus providing the necessary lifeline for the developing fetus.
For those women who have a history of miscarriages prometrium and pregnancy usually go together. The attending physician will usually prescribe the hormone replacement drug in either an oral form or in vaginal suppository. Women who take the oral form sometimes report nausea and/or dizziness as a side effect. Those taking it as a suppository do not seem affected in the same manner. However, there appear to be few, if any, complications for the unborn baby.
Some women taking prometrium during pregnancy worry that they might miss a miscarriage. In other words, prometrium might cause a naturally occurring miscarriage to not take place as in the case of a malformed fetus. In this situation, prometrium will not prevent the miscarriage. Prometrium works only to "hold" the pregnancy if it is a healthy, normal pregnancy to start with. Nature will take its course if the fetus is not viable and prometrium will not interfere with this process.
I found this on the Internet also you can have a miscarriage at any stage of your pregnancy, the fact that your in your second trimester doesn't nessiserily mean anything but it just means your chances go down slightly but if you are already at an increased risk then your not out of the red zone, hope everything goes ok for u xxx
The placenta takes over progesterone production at 10-12 weeks. Your risk for miscarriage goes down at that point and when you hear the babys heartbeat. I took progesterone in all three of my pregnancies with no problems. Good luck.