Ethinyl estradiol and levonorgestrel are hormones that affect the ovulatory and menstrual cycle of women. Ethinyl estradiol and levonorgestrel prevent ovulation (the release of an egg from an ovary), therefore preventing the possibility of pregnancy. Seasonale may also inhibit pregnancy by causing the cervical mucous to thicken, which makes it harder for sperm to move toward the uterus, and reducing the likelihood of attachment of a fertilized egg to the uterus.