Fertile mucus is present in the woman's body during the few days before ovulation, as the ova are ripening. This mucus is produced by the cervix, and flows down the vagina to the outside of the woman's body. The purpose of the mucus is to protect and nourish the sperm on their journey to the egg. The vaginal canal is normally acid. Semen is alkaline. Sperm die in an acid environment. The fertile mucus is alkaline, like the semen, and so makes the sperm's journey possible.

Even without ejaculation, sperm are present in the small amount of fluid produced by a tiny gland in the man's body called the Cowper's gland. Cowper's fluid leaks out of the penis during sexual activity. Therefore sperm are often present before ejaculation. The presence of sperm in the Cowper's fluid may be one reason for the ineffectiveness of withdrawal as a method of birth control. Another reason may be the leaking of a drop of seminal fluid before withdrawal occurs. The first drop of seminal fluid may contain millions of sperm. In addition, even without penetration of the man's penis inside the woman's vagina, pregnancy is possible. During the woman's fertile, wet, time, the tiny, microscopic sperm can swim from outside the vagina, into the vaginal opening, up the vagina, into the uterus, and into the fallopian tubes. There the sperm may fertilize the ovum, and pregnancy may begin. For this reason, during the woman's fertile time, pregnancy is possible with only genital contact. This means, touching of the penis to the vaginal area.