Cervical fluid, sometimes called cervical mucus, is something that all women have. It is quite different from the fluid produced during arousal. Cervical fluid helps sperm swim from the vagina, through the cervix, and into the uterus during the fertile time.
A few days before ovulation, the cervix produces a very slippery, wet, stretchy fluid resembling egg whites. This fluid can allow sperm to live for up to six days inside a woman's body. This means that a couple could have sex several days before ovulation occurs and the sperm could live long enough to meet the egg when it arrives days later. After ovulation has occurred and the fertile time is over, the fluid turns dry, pasty, and hostile for sperm.
By keeping track of what the fluid is like each day, a woman can zero-in on days with the wet, stretchy fluid. "By watching the fluid sign, a woman will know when ovulation is approaching," says Wodzinski. "These are the days that the couple should have intercourse to maximize the chance of pregnancy." On the flip side, if a woman notices that her fluid is always pasty and dry, she can point this out to her doctor as a possible problem.