Masturbation may increase fertility during sexual intercourse. In females, it can regulate the conditions of the vagina, cervix and the uterus. This can either increase or decrease the chance of conception. Whether the chance is increased or decreased depends on the timing of the masturbation. This timing is a subconscious decision. If she has intercourse with more than one male, it favors the chances of one or the other male's sperm reaching her egg.