One-half of the participants who qualify and wish to take part in the ongoing study will be randomized (assigned by chance, like the flip of a coin) to receive Endometrin® and an intramuscular injection of PIO every third day. One-half will be randomized to receive an intramuscular injection of PIO every day. This study is a type of study called an "open label," assessor-blind study. This means that you and your doctor will know which treatment you are assigned and receive; however, the person analyzing the information obtained from the study will not know which patients received which study treatments.