During labour the membranes and placenta become separated and expelled, but while the expulsion of these takes place after the child is born, the entire separation does not occur at any one period. During the first stage of labour the membranes in the lower portion of the uterus, in the part termed the lower uterine segment, become detached. The placenta, if placed partly in this segment, a condition known as placenta prsevia, becomes also separated. The rest of the membranes and placenta do not become separated until after childbirth, and this is followed by their expulsion as a whole.