in general

Pregnancy is the carrying of one or more offspring in an embryonal or fetal stage of development by femmale fetus, including humans, inside their bodies, between the stages of conception and birth. In a pregnancy, there can be multiple gestations (for example, in the case of twins, triplets). Human pregnancy is the most studied of all mammalian pregnancies. Childbirth usually occurs about 38 weeks from fertilization, i.e. approximately 40 weeks from the start of the last menstruation. Thus, pregnancy lasts about nine months, although the exact definition of the English word “pregnancy” is a subject of controversy. The medical term for a pregnant female is gravida, although this term is rarely used in common speech. The term embryo is used to describe the developing human during the initial weeks, and the term fetus is used from about two months of development until birth. A woman who is pregnant for the first time is known as a primgravida or "gravida 1", while a woman who has never been pregnant is known as "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 somewhat 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). During the second trimester the development of the fetus can start to be monitored and diagnosed. The third trimester often marks the beginning of viability, or the ability of the fetus to survive, with or without medical help, outside of the mother's womb.