Miscarriage, or spontaneous abortion, is the unintended loss of a fetus before the 20th completed week of pregnancy. In an incomplete miscarriage (also called an incomplete or missed spontaneous abortion), all or some of the fetal tissue stays in the uterus after a pregnancy miscarries.
An incomplete miscarriage usually requires treatment to make sure the uterus is cleared of all tissue. In the earlier weeks after conception, medicines can be used to make the uterus push out its contents. Or a procedure called dilation and curettage (D&C) is used to empty the uterus.
The birth of a fetus without a heartbeat after 20 weeks of pregnancy is known as a stillbirth.
WebMD Medical Reference from Healthwise