Birth refers to the process of a baby being expelled from its mother’s uterus, followed by the expulsion of the placenta. In humans, birth is expected to occur 38 weeks after conception, although it can happen at any point during gestation. The timing and method of birth are relevant to lifespan human development because they can have profound effects on the baby’s quality of life from infancy through adulthood. This entry presents a biological definition of birth, possible complications that may arise during the process, and postpartum impacts on both mother and child.