Is Healthy Pregnancy Possible While Having Low Progesterone Levels?

My duagter is approx. six weeks preg. Her HCG is 21,000 but her progesterone is only 5. I had a luteal phase defect and had 10 miscarriages in the 80's. They're starting her on a progesterone supplement today. What are her chances of carrying this baby. They measured the sac at six weeks a few days ago.