Maternal risk factors comprised diabetes or gestational diabetes (3/20), recurrent pregnancy losses or intrauterine fetal death (2/20), thrombus in the umbilical artery or vein (2/20), maternal infection (1/20), twin pregnancy (1/20), placental abruption (1/20), and protein S deficiency (1/20). Here, PROS1 is linked to placental abruption.