Pregnancy is when a woman or female mammal has an unborn baby inside her. During pregnancy, a female is called "pregnant". A human pregnancy is about 38 weeks long, from conception to childbirth. Usually the mother has one baby at a time. Sometimes the mother has two babies at one time. Two babies are called twins. The mother can have three or more babies at one time. This does not happen very often in humans.[1] Aboout one in 85 pregnancies are of twins, and about one in 7,000 are of triplets.
Some people have trouble becoming pregnant. This is called infertility. Women and men with infertility may take drugs or have surgery to help a pregnancy start. Some people use treatments that are not natural, like in vitro fertilization, to become pregnant with the help of a doctor.