It’s basic biology. During sexual intercourse, a man ejaculates semen into a woman’s vagina. Semen is a white, sticky fluid that contains sperm, which can fertilize a female’s egg. The sperm swim through the female’s cervix and uterus, into her fallopian tubes, where eggs are released from her ovaries. If she has recently ovulated, or released an egg, then the sperm can swim into the egg and start a pregnancy. Ovulation happens once a month.

           An egg can live and be fertilized for about 24 to 36 hours. Sperm can live for up to five days.

           Once the sperm and egg connect it eventually lands in the uterus after traveling through the fallopian tubes. The lining of the uterus is full of blood and tissue. This nutrient-rich lining gives the egg something to attach to. Once that happens, the pregnancy has taken root. It soon develops into an embryo. The embryo, in turn, becomes a fetus over the next nine months.

           If egg and sperm fail to connect, the egg dies. With no pregnancy, the lining of the uterus disintegrates. This lining becomes a female’s period or menstruation.