Pregnancy, also known as gestation, is a period of reproduction during which the female carries one or more live offspring from the initial fertilization of the egg, as a result of sexual intercourse or assisted reproductive technology, up until birth. In the case of humans, pregnancy is typically broken up into three major stages, also called trimesters, lasting fourteen weeks each for a total of 40 to 42 weeks. In other mammals, this process can last anywhere in length from twelve days, in the case of opossums, up to nearly two years, in the case of elephants.