口交
Oral sex alone cannot result in pregnancy and heterosexual couples may perform oral sex as their method of contraception. For conception to take place, sperm from the penis must enter the uterus and fallopian tubes and fertilize the female's egg. In humans, there is no connection between the gastrointestinal system and the reproductive system, and sperm ingested by the woman would be killed and broken down by acids in her stomach and proteins in the small intestine. The breakdown products are then absorbed as a negligible quantity of nutrients. However, there is a potential risk of pregnancy if semen comes in contact with the vaginal area in some way, such as semen in the ejaculate finding its way onto fingers, hands, or other body parts, which then comes in contact with the vaginal area.