When a a woman with RhD negative blood is exposed to RhD positive blood in pregnancy she can develops an immune response to it and develop anti D antibodies. In later pregnancies, anti-D antibodies can cross the placenta, causing rhesus haemolytic disease in the Rh positive fetus, and is worsened with subsequent pregnancies.Rhesus disease can largely be prevented by giving an injection of a medication called anti-D immunoglobulin to the Rh negative mother.
The anti-D immunoglobulin neutralizes any RhD positive antigens that may have entered the mother’s blood during pregnancy. If the antigens have been neutralized, the mother’s blood won't produce antibodies.
It is often given both during and following pregnancy.
- Following potentially sensitizing events in pregnancy, it is recommended that anti-D Ig should be administered as soon as possible and always within 72 hours of the event.
- If, exceptionally, this deadline has not been met, some protection may be offered if anti-D Ig is given up to 10 days after the sensitizing event.
- It may also be used when Rh negative people are given Rh positive blood.
- Anti D Immunoglobulinis also used to treat idiopathic thrombocytopenic purpura (ITP) in people who are Rh positive.
- Invasive prenatal diagnosis - e.g, amniocentesis, chronic villus biopsy.
- Antepartum haemorrhage.
- External cephalic version of the fetus (including attempted).
- Ectopic pregnancy.
- Evacuation of molar pregnancy.
- Intrauterine death and stillbirth.
- Intrauterine procedures (eg, insertion of shunts, embryo reduction).
- Miscarriage or threatened miscarriage after 12 weeks of gestation.
- Therapeutic termination of pregnancy.
- Delivery - normal, instrumental or caesarean section.
Use of anti-D in pregnancy in Rh–ve mothers
- Give anti-D 500U at 28 and 34 weeks to rhesus negative women ( antenatal sensitization falls from 0.95% to 0.35%).
- Anti-D may still be detectable in maternal blood at delivery.
- Still give postnatal anti-D.
- one-dose treatment: where Rh negative mothers are given an injection of immunoglobulin at some point during weeks 28 to 30 of pregnancy
- a two-dose treatment: where Rh negative mothers are given two injections; one during the 28th week and the other during the 34th week of your pregnancy
There doesn't seem to be any difference in the effectiveness between the one-dose or two-dose treatments, and different clinics and doctors follow different protocols.
Postnatal Administration Of Anti-D immunoglobulin
- At least 500 IU of anti-D should be given to every non-sensitised RhD-negative woman, within 72 hours of delivering a rhesus-positive infant.
- If the baby is stillborn (and no sample can be obtained from the baby), anti-D should be given.
- 37% of Rh–ve women give birth to Rh–ve babies and these women do not need anti-D.
The Kleihauer test, is a blood test used to measure the amount of fetal hemoglobin transferred from a fetus to a mother's bloodstream and should be done on all eligible patients for Anti D Ig.
500U anti-D can suppress immunization by up to 4 mL of fetal red cells (8 mL of fetal blood), but 1% of women have transplacental haemorrhage (TPH) of >4mL, especially after manual removal of placenta, and with caesarean section. A Kleihauer test is especially important in stillbirth, as massive spontaneous transplacental hemorrhage can be the cause of fetal death. Where >4 mL TPH is suggested by the Kleihauer screen, a formal estimation of the TPH volume is required and 500U anti-D given for every 4mL fetal cells transfused (maximum 5000U anti-D at 2 IM sites/24h).
Mode of Administration: Anti D Immunoglobulin is given by injection into muscle or a vein. A single dose lasts 2 to 4 weeks. and therefore is needed in each pregnancy.