Cervical mucus is secreted by glandular cells that are present in the cervix. This mucus protects the uterus from invasion by bacteria present in the vagina. It also plays an important role in infertility. The cervical mucus, in response to the estrogen hormone, becomes thin and elastic at the time of ovulation. This allows the sperm to travel through the cervix and the uterus to reach the egg in the fallopian tube. It also helps the sperm to stay alive in the cervix for a longer period of time. A thick and dense mucus could prevent the passage of sperm through the cervix.