Rhesus status and anti-D immunoglobulin

Administration of anti-D immunoglobulin to women at risk of Feto-maternal haemorrhage (FMH) reduces the risk of sensitisation.

Feto-maternal haemorrhage (FMH):

• Is most common in the third trimester, during childbirth and following events associated with FMH. Such events include medical interventions (chorionic villus sampling, amniocentesis, external cephalic version), terminations, late miscarriages, APH and abdominal trauma
• Can occur in the absence of an observed potentially sensitising event
• Causes alloimmunisation

Sensitisation:

• Has no effect on the mother and usually no adverse effect on the fetus in the primary pregnancy during which it occurs
• Is dependent on the volume of fetal blood entering the maternal circulation and the volume of the mothers immune response
• Is greatest with the first pregnancy (with the same father) and reduced with subsequent pregnancies
• Once occurred is irreversible

The immune response is:

• Usually not detected in the first pregnancy
• Faster and greater in subsequent pregnancies
• Causes fetal anaemia which in utero leads to heart failure, hydrops foetalis and intrauterine death. Neonatally haemolytic disease of the newborn ensues causing kernicterus