What is?

Understanding how pregnancy happens is important. If you want to avoid pregnancy, it helps to know when a woman is most likely to get pregnant, and when she is not. If you are trying to become pregnant, it is important to know when getting pregnant is most likely and the different ways it can happen.

Whether you are trying to avoid pregnancy, trying to get pregnant, or are just curious, you may have lots of questions. Here are some answers about how pregnancy happens.

Pregnancy is the fertilization and development of one or more offspring, known as an embryo or fetus, in a woman's uterus. In a pregnancy, there can be multiple gestations. Childbirth usually occurs about 38 weeks after conception; in women who have a menstrual cycle length of four weeks, this is approximately 40 weeks from the start of the last normal menstrual period. 

Human pregnancy is the most studied of all mammalian pregnancies. Conception can be achieved through sexual intercourse or assisted reproductive technology. An embryo is the developing offspring during the first 8 weeks following conception, and subsequently the term fetus is used until birth. In many societies' medical or legal definitions, human pregnancy is somewhat arbitrarily divided into three trimester periods, as a means to simplify reference to the different stages of prenatal development. 

The first trimester carries the highest risk of miscarriage (natural death of embryo or fetus). During the second trimester, the development of the fetus can be more easily monitored and diagnosed. The beginning of the third trimester often approximates the point of viability, or the ability of the fetus to survive, with or without medical help, outside of the uterus.