Blood group and Rh incompatibility Flashcards
Discuss pathophysiology of ABO incompatibility
This can occur in first and subsequent pregnancies.
Mother is blood group O and baby A, B or AB.
If the mother is exposed to the foetal blood, she will develop anti-A and anti-B IgG (maternal sensitisation). She may also just have anti-A/B IgG naturally occurring.
These cross the placenta and attack the foetal erythrocytes causes agglutination and thus haemolysis (get haemolytic anaemia).
Occurs in 20% of pregnancies but only 1-2% present with haemolysis.
These antibodies can be naturally occurring (which is why it can occur in first pregnancy too) or acquired after sensitisation.
Foetal consequences of haemolytic disease of the newborn
May have spontaneous abortion early on in pregnancy.
Early jaundice–> can get kernicterus, which predisposes to CP.
Also at risk of late onset anaemia.
Pathophysiology of Rhesus disease
Occurs in mothers who are Rh negative and baby is Rh positive. Only occurs in second pregnancy, after mom has been sensitised (as in first pregnancy only makes IgM which can’t cross placenta).
Sensitising events include C/S, ECV, amnio, miscarriage, TOP, ectopic, foeto-maternal bleed.
In next pregnancy, mom had created anti-D IgG, which crosses placenta and attacks foetal erythrocytes.
Management of a Rh negative woman in pregnancy
a) If mom does not have any atypical antibodies (anti-IgG):
Mother is tested at 26, 32 and 38 weeks due to the possibility of sensitisation during this time. If none develop, she can be delivered at term. After delivery (within 72 hours), she is given 100ug Rhogam IMI if the foetus is Rh positive (or if Rh status unknown).
RHogam should also be given in RH negative moms after an abortion or ectopic.
b) If the mom does have anti-D atypical antibodies:
Check father’s Rh status and gestational age.
Do mom’s antibody titre every 2 weeks.
If titre>1.8: do US of middle cerebral artery (lookout velocity of flow, tells you if foetus is anaemic). If peak systolic velocity (PSV) >1.5 SDs of the mean then can presume there is foetal anaemia. If normal, then repeat 1-2 weekly to keep checking it’s <1.5.
If it is >1.5:
If baby >34/40 can deliver.
If <34/40: give BMZ and review PSV in 48 hours after steroids. If now <1.5 then can review in 1/52. If worse, need to deliver baby.
In really small babies–> need to do intrauterine blood transfusion (transfuse into umbilical cord). Continue MCA US monitoring and repeated transfusions if necessary until able to deliver.
If no facilities to do transfusion, give BMZ and deliver baby prematurely.
What is PSV and what is it’s clinical benefit in Rh disease?
What do we do in mothers >35 weeks?
PSV= peak systolic flow
Measured by doing US of MCA and working out how many SDs of mean it is by plotting it on a chart.
It is valuable in determining if foetal anaemia from Rh disease is problematic or not.
It is only reliable up until 35 weeks, thereafter it isn’t reliable (so you would just use the anti-D IgG titre).
If >35 weeks, you check titre and if >1:32 then deliver baby. If <1:32 then can follow up in 1 weeks and aim to deliver at 38.
Indications to give Rhogam
After delivery Ectopic pregnancy Procedures like ECV or amnio APH Miscarriage All need to be within 72 hours of this exposure.
