Rhesus-D Negative → 15% of mothers. Need to consider possibility that child will be rhesus positive. If blood from baby enters the mother’s blood stream, the mother’s immune system will recognise the rhesus-D antigen as foreign, and produce antibodies against it. This causes mother to become sensitised to rhesus-D antigens.
Sensitisation does not usually cause problems during first pregnancy. In subsequent pregnancies, the mother’s anti-rhesus-D IgG antibodies can cross the placenta into the fetus. If fetus is rhesus-D positive, haemolysis of the fetuc RBC’s can occur → haemolytic disease of the newborn.
Sensitisation → process whereby fetal red blood cells (RhD-positive) enter the maternal circulation, where the mother is RhD-negative. The fetomaternal haemorrhage (FMH) can cause antibodies to form in the maternal circulation that can haemolyse fetal red blood cells.
Kleihauer Test (ONLY USED >20 WEEKS) → used after any sensitising event past 20 weeks gestation, to see how much fetal blood has passed into the mother’s blood, and determine whether further doses of anti-D are required.
Management Plan
Antenatal Care → anti-D at 28 and 34 weeks.
One dose of 1500 IU at 28 weeks or two doses of 500 IU at 28 and 34 weeks.
Prevention of Sensitisation → giving IM anti-D injections to rhesus-D negative women. There is no way to reverse sensitisation once it has happened, hence prophylaxis is essential.
Anti-D medication works by attaching itself to the rhesus-D antigens on the fetal RBCs in the mothers circulation, causing them to be destroyed. This prevents the mother’s immune system recognising the antigen and creating it’s own antibodies to the antigen.
Also given at times sensitisation may occur (WITHIN 72 HOURS) → antepartum haemorrhage, amniocentesis procedures, surgical management of ectopic or miscarriage, abdominal trauma, vaginal bleeding (>12w or <12w+heavy).
After Sensitising Event (within 72 hrs):
<20 weeks: 250 IU
20 weeks: kleihauer test + 500 IU
Delivery → if baby is found to be Rh +ve at birth (via cord sample), mother should recieve 500 IU anti-D <72 hrs.