Congenital fibrinogen deficiency is a rare hereditary coagulation disorder that occurs when the body cannot produce enough fibrinogen (also known as factor I). Fibrinogen helps to stop bleeding by contributing to clot formation. Congenital fibrinogen deficiency is an umbrella term for various diseases of this nature: Afibrinogenaemia (the complete lack of fibrinogen), hypofibrinogenaemia (low levels of fibrinogen), dysfibrinogenaemia (the fibrinogen does not work properly) and hypodysfibrinogenaemia (a combined defect with low levels of fibrinogen that also does not work properly).