"Progesterone is one of the hormones in our bodies that stimulates and regulates various functions. Progesterone plays a role in maintaining pregnancy. The hormone is produced in the ovaries, the placenta (when a woman gets pregnant) and the adrenal glands. It helps prepare your body for conception and pregnancy and regulates the monthly menstrual cycle. It also plays a role in sexual desire."
I had never heard of a women having low progesterone. After my first I waited a year to get pregnant again, the first thing I did when I found out I was pg was call my Dr. He had me come in to have my progesterone checked. Typically during pregnancy they like to see your levels at 20, mine were at 9. Although this wasn't my answer in the end, I feel like progesterone is a huge place for anyone suffering repeated losses to start. It such a simple fix, pills, cream, or a suppository are the most common methods of use(i've heard of injections as well, but I don't know how common that is). There is some debate as to which is better, I've used both pills and suppositories during my pregnancies and found pills to be the easier method since the suppositories require 30 minutes of lay down after insertion.
Among the debate is when to start and when to stop taking it. Obviously If You know your progesterone is low you should start taking it ASAP. Many suggest after ovulation even. Do you know though? I didn't. I started taking it at 10 weeks during the pregnancy in question, 2 days before my missed period during my next pregnancy, and my current pregnancy I started at 4 weeks, give or take. The first two were losses, and I've been off of the progesterone for quite some time at this point in my current pregnancy. My suggestion is to become familiar with your doctor and most importantly your body and you can make the best decision for yourselves.
As far as stopping, most Practitioners will humor you and allow you to continue to take it past the 12 week mark, however if your baby is growing properly up to that point your placenta will take over the job of the progesterone and it becomes taking the meds for the sake of taking it. I stopped at 12 weeks this time, reluctantly, but my dr assured me that it wasn't necessary anymore. Talk to your doctor about how you really feel about it. A good relationship with your doctor is priceless when you are a repeat miscarriage offender.
Ok so like I said in the end progesterone isn't my real underlying issue, but it was an issue to look for in a big way.
** And as a side note I was told during this pregnancy that Progesterone is the little devil that causes morning sickness, which explains why I've never suffered from morning sickness! So if you're puking your guts up, take heart, thats a good sign.. :-\