Sexual intercourse, commonly known as "sex", occurs when a male and female decide to engage in the emotionally and physically intimate act. After foreplay in which both people get sexually aroused, the male places his penis inside the female's vagina . A couple usually has sexual intercourse for pleasure and sexual satisfaction. The biological function of sexual intercourse is to lead to pregnancy.

WHAT HAPPENS BEFORE SEXUAL INTERCOURSE?

Most couples have foreplay before intercourse. Foreplay might include hugging, kissing, touching each other's genitals, and touching a woman's breasts.

Biologically, sexual intercourse can only happen when a male has an erection . Emotionally, sex is much more pleasurable when both partners are sexually excited. In females, that excitement shows up in her body during foreplay as an increase in fluids and secretions that are released from her vagina and cervix. These secretions make the vagina more slippery and wet, which makes it easier for the male to insert his penis. As the male becomes more excited, his penis fills with extra blood. That makes it grow longer, extend upward, and become hard. When the male's penis is hard and the female's vagina is wet, intercourse can occur.

WHAT HAPPENS DURING INTERCOURSE?

When a couple decides to have intercourse, the male inserts his penis into the female's vagina. They can have intercourse in many different positions including the boy on top, the girl on top, or facing each other on their sides. The couple moves together until one or both of them reaches orgasm. This can take anywhere from several seconds to several minutes.

Not all females have an orgasm during intercourse. Other girls find they need more or different stimulation (like oral sex) to have one.

WHAT ARE THE CHANCES OF GETTING PREGNANT AFTER HAVING INTERCOURSE?

Most couples have intercourse for sexual satisfaction, but its main biological purpose is to lead to pregnancy. When a man has an orgasm, sperm in his semen are released into the vagina. The sperm swim up through the uterus and fallopian tubes to try to meet an egg and fertilize it.

Unless you use birth control, it's only a matter of time before you become pregnant. If you are having unprotected sexual intercourse, there's a 20% chance that you will be pregnant within 1 month. If you continue having unprotected intercourse, your chances of getting pregnant rise dramatically. After 6 months, there is a 50% chance you will be pregnant, and after a year it rises to 90%. So if you are having unprotected sex, you will get pregnant; the only question is when.