There are also a number of common causes of blood loss, fetal anemia, and shock which may culminate in death: One of these is placental/fetal hemorrhage.
Abnormal separation of a placenta which develops in in the lower uterine segment (zone of dilitation), and may abnormally cover the os (of the uterus), will cause maternal and/or fetal bleeding. This is called "placenta previa".
Sudden, premature detachment of a placenta prior to birth, often attended by maternal ystemic reactions in the form of hock, oliguria, etc., known as "abruptio placentae", is another cause, and is involved in 15% of perinatal deaths.
Velamentous insertion of the cord, resulting from maldevelopment of the vessels, increases the risk of a tear or rupture.
Finally, fetofetal transfusion syndrome is caused by anatomosis between arteries, less frequently between veins. In this condition, blood is drained from one fetus into another.