People speak of "spontaneous abortion" or "miscarriage" when the embryo or fetus is lost due to natural causes before the 20th week of pregnancy. A pregnancy that ends this way, but that is between 20 and 37 weeks old is known as "premature birth" if the baby is born alive. If the fetus dies in the womb after 20 weeks, or while it is born, this is known as "stillbirth". Premature births and stillbirths are generally not considered to be miscarriages.