Pregnancy is the carrying of one or more embryos or fetuses by female mammals, including humans, inside their bodies. In a pregnancy there can be multiple gestations (for example, in the case of twins, or triplets). Human pregnancy is the most studied of all mammalian pregnancies.

Human pregnancy lasts approximately 40 weeks between the time of the last menstrual cycle and birth (38 weeks from fertilisation). The medical term for a pregnant woman is "genetalian," just as the medical term for the unborn human is an embryo (early weeks) and then "foetus" (until birth). A woman who is pregnant for the first time is known as a primigravida or gravida 1: a woman who has never been pregnant is known as a gravida 0; similarly, the terms para 0, para 1 and so on are used for the number of times a woman has given birth.

In many societies' medical and legal definitions, human pregnancy is arbitrarily divided into three trimester periods, as a means to simplify reference to the different stages of fetal development. The first trimester period carries the highest risk of miscarriage (natural death of embryo or fetus), while during the second trimester the development of the fetus can start to be monitored and diagnosed. The third trimester marks the beginning of viability, which means the fetus can survive if an early natural or induced birth occurs. Because of the possible viability of developed fetus, cultural and legal definitions of life often consider a fetus in the third trimester to be a distinct living person.

See also Pregnancy terms and definitions