Foetal-maternal haemorrhage may be defined as the loss of foetal blood cells
into the maternal circulation. It takes place in normal pregnancies
as well as when there are obstetric or trauma related complications to pregnancy.
Normally the maternal circulation and the foetal circulation are kept from direct contact with each other, with gas and nutrient exchange taking place across a membrane in the placenta made of two layers, the syncytiotrophoblast and the cytotrophoblast. Foetal-maternal haemorrhage occurs when this membrane ceases to function as a barrier and foetal cells may come in contact with and enter the maternal vessels in the decidua/endometrium
It is estimated that less than 1ml of foetal blood is lost to the maternal circulation during normal labour in around 96% of normal deliveries. The loss of this small amount of blood may however be a sensitising event and stimluate antibody production to the foetal red blood cells, and example of which is Rhesus disease of the newborn.
Causes of increased foetal-maternal haemorrhage are seen as a result of trauma, placental abruption or may be spontaneous with no cause found.
Up to 30mls of foetal-maternal transfusion may take place with no significant signs or symptoms seen in either mother or foetus. Loss in excess of this may result in significant morbidity and mortality to the foetus. Foetal-maternal haemorrhage is one cause of interuterine death (IUD).
If ongoing and rapid haemorrhage is occurring then immediate delivery of the foetus may be indicated if the foetus is sufficiently developed. If the haemorrhage has already occurred and now stopped, an inutero transfusion of red cells to the foetus may be recommended.