Cervical mucus also known as cervical fluid is a vaginal discharge produced by the glands in the cervix. The cervix is a passage that connects the vagina to the uterus. The color, texture and consistency of your CM changes through out your menstrual cycle.
After ovulation, the hormone progesterone causes cervical mucus to become sticky and thick. This stops sperm (and any other foreign substance) from getting through to the uterus. As ovulation approaches, your cervical mucus changes from a consistency that's not sperm-friendly to a more fertile variety.
Egg white cervical mucus is the most fertile kind of cervical mucus, and it is frequently abbreviated as EWCM on fertility charts and in trying to conceive forums. While cervical mucus changes throughout a woman's cycle, EWCM is the most fertile and signals the best time to have sex for pregnancy.
Cervical mucus that doesn't ever become fertile is sometimes referred to as hostile cervical mucus. You may see fertile cervical mucus again right before your period. Some women notice that their cervical mucus becomes wet or almost egg white-like again right before menstruation. Obviously, this isn't a sign of impending ovulation. Women sometimes wonder if getting a lot of cervical mucus just before their period is a possible early pregnancy sign.