Crinone 8% (progesterone gel) is a specially formulated vaginal gel that contains the female hormone progesterone. Progesterone is important for ovulation and menstruation. Progesterone causes changes in the lining of your uterus, making it easier for a fertilized egg to attach to the uterus at the beginning of pregnancy. Progesterone then helps maintain the pregnancy until the placenta can provide its own hormonal support. Crinone is used in fertility treatment as part of IVF for women unable to get pregnant due to a lack of natural progesterone in the body. Unlike injectable progesterone, Crinone is applied into the vagina where it adheres to the vaginal walls and so is absorbed directly where is needed. This form of application avoids the local pain associated with intramuscular injections of progesterone.