Crinone is a gel that contains a hormone called progesterone, which prepares the lining of your uterus for implantation and pregnancy. Oftentimes, fertility medications affect your progesterone levels. You may be prescribed a progesterone supplement to make up for this decrease when it's time for the transfer. Crinone gel is inserted vaginally using an applicator. Some clinics or doctors may prescribe different forms of progesterone as an alternative.