Occult fetomaternal haemorrhage as a cause of fetal mortality and morbidity.

Spontaneous fetomaternal haemorrhage is an important, but usually overlooked, cause of perinatal mortality and morbidity. Although fetomaternal bleeding in the third trimester of pregnancy is common it is normally less than 0.1 ml. A fetal macrotransfusion (greater than 5 ml) is uncommon, but is important because it is insidious, unexpected and usually occurs in completely normal pregnancies. This paper analyses the perinatal mortality and morbidity associated with occult fetomaternal haemorrhage at the Royal Women's Hospital, Melbourne. It may lead to fetal distress before and during labour, unexplained stillbirth, or nonhaemolytic neonatal anaemia. A Kleihauer test on maternal blood will readily detect fetomaternal bleeding, and we describe a simple way of calculating the absolute volume of fetal red cells present. Greater awareness of the problem may eventually lead to diagnosis sufficiently early to permit effective treatment.