Blood grouping and red-cell alloantibodies in pregnancy

It is important to identify at risk pregnancies (Rhesus (Rh) negative women).

• anti-rhesus (anti-D) immunoglobulin should be given after delivery to all Rh-negative women where the baby's blood group cannot be determined (e.g. if macerated stillbirth). Also anti-D should be given to Rh-negative mothers following the birth of a Rh-positive infant, immediately or within 72 hours
• antenatal prophylaxis with anti-D: NICE now recommends that routine anti-D prophylaxis is offered to all non-sensitised pregnant women who are RhD negative
  • can be given as two doses of anti-D immunoglobulin of 500 IU (one at 28 weeks and one at 34 weeks gestation), as two doses of anti-D immunoglobulin of 1000-1650 IU (one at 28 weeks and one at 34 weeks gestation), or as a single dose of 1500 IU either at 28 weeks or between 28 and 30 weeks gestation
• anti-D has the effect of mopping up any rhesus positive cells from the infant in the maternal circulation, and preventing the mother from mounting an immune response. In this way, future pregnancies are protected
  
  
• other uses of anti-D during pregnancy in Rh-negative mothers:
  • if threatened abortion in Rh-negative mother - note that Anti-D Ig is no longer necessary in women with threatened miscarriage with a viable fetus and cessation of bleeding before 12 weeks' gestation (1)
    • "..evidence that women are sensitised after uterine bleeding in the first 12 weeks of pregnancy where the fetus is viable and the pregnancy continues is scant though there are very rare examples.. Against this background, routine administration of anti-D Ig cannot be recommended. However it may be prudent to administer anti-D Ig where bleeding is heavy or repeated or where there is associated abdominal pain particularly if these events occur as gestation approaches 12 weeks. The period of gestation should be confirmed by ultrasound..."
  • during any manoeuvres in pregnancy (uterine procedures e.g. amniocentesis, chorionic villous sampling, external cephalic version), also after antepartum haemorrhage, abdominal trauma, postpartum (as described above)
• other situations where anti-D may be used:
  • anti-D should also be given in management of an ectopic pregnancy in a Rh-negative woman
  • anti-D should also be given to all Rh-negative women following any other potentially sensitising episode (e.g. surgical termination of pregnancy, abortion, stillbirth)
    
    
• in pregnancies which are already affected the anti rhesus antibody level may be assessed at intervals from the third trimester; extent of disease may be measured with amniocentesis if the antibodies are worsening
• if additional prophylactic doses of anti-D are given at 28 and 34 weeks then the risk of sensitization is reduced from 1.12% to 0.28% (2)

Notes (3):

• routine anti-D prophylaxis is offered to all non-sensitised pregnant women who are RhD negative
• women should be screened for atypical red cell alloantibodies in early pregnancy and again at 28 weeks regardless of their RhD status
• pregnant women with clinically significant atypical red cell alloantibodies should be offered referral to a specialist centre for further investigation and advice on subsequent antenatal management
• if a pregnant woman is RhD-negative, consideration should be given to offering partner testing to determine whether the administration of anti-D prophylaxis is necessary

Reference

• (1) Royal College of Obstetricians and Gynaecologists. Use of Anti-D Immunoglobulin for Rh Prophylaxis (22) - Revised May 2002.
• (2) Mayne S (1997). BMJ, ii, 1588.
• (3) NICE (2008). Antenatal care.