Understanding a Short Luteal Phase & Progesterone Levels After Miscarriage

Question
I am 25 and have no children.  I have had three miscarriages in less than a year and the date of my last period was 4-5-06.  I was recently pregnant last month and went in for blood work and a urine test.  The urine test was positive and the blood test came back indecisive.  My progestorone was 3.3 at 2 weeks of pregnancy.  My doctor immediately put me on 10 mg of progesterone to be taken once daily.  Now that I have started my period, he is telling me to start taking it again after my peroid ends.  I do not understand this since I know that progesterone is supposed to be the dominant horomone in the second half of the cycle.  Also, I have read that it can dry up cervical fluid, which is need for sperm to travel through.  I think it would make more sence to start taking it after I know I have ovulated (I chart my temps.)  What do you think about all of this?  

Answer
Progesterone has many different uses. It has been found that it help reduce miscarriages if the value is low (less than 9). We often give progesterone suppositories (rather than pills0 every day until you are pregnant  and we continue them until you have reached 12 weeks gestation. Another use of progesterone is to induce a period (10mg twice  day for 5 days) and your period starts within 10 days. The progesterone you have in your body, is reponsible for changes in the second half of your cycle. It causes coiled arteries to form. If you do not become pregnant, your period will start around 28 days. If you do become pregnant,the progesterone will maintain the pregnancy until the placenta is formed. There are many other advantages to taking progesterone. I would suggest that you follow the instructions of your doctor.