Rhesus negative pregnancy

along with the ABO system the Rhesus system is the most important antigen found on red blood cells. The D antigen is the most important antigen of the rhesus system
around 15% of mothers are rhesus negative (Rh -ve)
if a Rh -ve mother delivers a Rh +ve child a leak of fetal red blood cells may occur
this causes anti-D IgG antibodies to form in mother
in later pregnancies these can cross placenta and cause haemolysis in fetus
this can also occur in the first pregnancy due to leaks

test for D antibodies in all Rh -ve mothers at booking
NICE (2008) advise giving anti-D to non-sensitised Rh -ve mothers at 28 and 34 weeks
the evidence base suggests that there is little difference in the efficacy of single-dose (at 28 weeks) and double-dose regimes (at 28 & 34 weeks). For this reason the RCOG in 2011 advised that either regime could be used 'depending on local factors'
anti-D is prophylaxis - once sensitization has occurred it is irreversible
if event is in 2nd/3rd trimester give large dose of anti-D and perform Kleihauer test - determines proportion of fetal RBCs present

Anti-D immunoglobulin should be given as soon as possible (but always within 72 hours) in the following situations:

delivery of a Rh +ve infant, whether live or stillborn
any termination of pregnancy
miscarriage if gestation is > 12 weeks
ectopic pregnancy (if managed surgically, if managed medically with methotrexate anti-D is not required)