Haemorrhage into maternal circulation

**Definition:** Fetal-maternal haemorrhage occurs when the trophoblastic lining of the placenta fails to act as a barrier and allows fetal blood cells to enter the maternal circulation.

**Long definition:** Fetal-maternal haemorrhage occurs when the trophoblastic lining of the placenta fails to act as a barrier and allows fetal blood cells to enter the maternal circulation. The most significant blood loss occurs in the third trimester of pregnancy, or during labour and delivery. Examples of factors associated with haemorrhage include: abdominal trauma, caesarean section, amniocentesis, and intrauterine transfusion. If bleeding occurs in close proximity to delivery it can be identified by the Kleihauer-Betke (KB) test on the maternal blood that recognizes fetal cells by their resistance to alkali denaturation.