20 or older than 35 are at greater risk Risk factors for placental abruption include disease, trauma, history, anatomy, and exposure to substances. The risk of placental abruption increases sixfold after severe maternal trauma. Anatomical risk factors include uncommon uterine anatomy (e.g. bicornuate uterus), uterine synechiae, and leiomyoma. Substances that increase risk of placental abruption include cocaine and tobacco when consumed during pregnancy, especially the third trimester. History of placental abruption or previous Caesarian section increases the risk by a factor of 2.3. Pathophysiology In the vast majority of cases, placental abruption is caused by the maternal vessels tearing away from the decidua basalis, not the fetal vessels. The underlying cause is often unknown. A small number of abruptions are caused by trauma that stretches the uterus. Because the placenta is less elastic than the uterus, it tears away when the uterine tissue stretches suddenly. When anatomical risk factors are present, the placenta does not attach in a place that provides adequate support, and it may not develop appropriately or be separated as it grows. Cocaine use during the third trimester has a 10% chance of causing abruption. Though the exact mechanism is not known, cocaine and tobacco cause systemic vasoconstriction, which can severely restrict the placental blood supply (hypoperfusion and ischemia), or otherwise disrupt the vasculature of the placenta, causing tissue necrosis, bleeding, and therefore abruption. In most cases, placental disease and abnormalities of the spiral arteries develop throughout the pregnancy and lead to necrosis, inflammation, vascular problems, and ultimately, abruption. Because of this, most abruptions are caused by bleeding from the arterial supply, not the venous supply. Production of thrombin via massive bleeding causes the uterus to contract and leads to DIC. The accumulating blood pushes between the layers of the decidua, pushing the uterine wall and placenta apart. When the placenta is separated, it is unable to exchange waste, nutrients, and oxygen, a necessary function for the fetus's survival. The fetus dies when it no longer receives enough oxygen and nutrients to survive. Diagnosis Placental abruption is suspected when a pregnant mother has sudden localized abdominal pain with or without bleeding. The fundus may be monitored because a rising fundus can indicate bleeding. An ultrasound may be used to rule out placenta praevia but is not diagnostic for abruption. The diagnosis is one of exclusion, meaning other possible sources of vaginal bleeding or abdominal pain have to