Amniotic fluid embolism occurs when amniotic fluid or fetal material enters the mother's bloodstream. Why this happens isn't well understood. A likely cause is a breakdown in the placental barrier, such as from trauma.

When this breakdown happens, the immune system responds by releasing products that cause an inflammatory reaction, activating abnormal clotting in the mother's lungs and blood vessels that can result in a serious blood-clotting disorder known as disseminated intravascular coagulation.

However, amniotic fluid embolisms are rare — and it's likely that some amniotic fluid commonly enters the mother's bloodstream during delivery without causing problems. It's not clear why in some cases this leads to amniotic fluid embolism.

Further research on what causes amniotic fluid embolisms is needed.

Sept. 11, 2015