Blood group, antibodies and rhesus prophylaxis — Rapid

Synopsis

Interpret maternal blood group and antibody results, prevent avoidable RhD alloimmunisation and escalate established red-cell alloimmunisation before fetal anaemia develops.

Determine ABO group, RhD status and red-cell antibodies at booking and repeat antibody screening at 28 weeks, regardless of RhD group.
Routine antenatal anti-D prophylaxis is for non-sensitised RhD-negative pregnancies: use the licensed local regimen of one dose at 28 to 30 weeks or two doses at 28 and 34 weeks.
Routine prophylaxis does not replace event-related prophylaxis after a qualifying sensitising event or postnatal anti-D when the newborn is RhD positive.
Give indicated anti-D as soon as possible and within 72 hours; if the deadline is missed, obtain transfusion advice because some benefit may remain rather than abandoning prophylaxis.
After 20 weeks, give at least 500 IU for a sensitising event and quantify fetomaternal haemorrhage so additional anti-D can cover a larger bleed.
Current NICE NG126 says no anti-D for ectopic pregnancy, miscarriage or threatened miscarriage up to 11+6 weeks; at 12+0 to 12+6 weeks, offer at least 250 IU after medical or surgical ectopic pregnancy or miscarriage and consider it for heavy or recurrent threatened-miscarriage bleeding.
Prophylactic anti-D prevents new immune anti-D; it cannot remove established maternal anti-D or treat a fetus already affected by haemolysis.
When non-invasive fetal RHD testing shows an RhD-negative fetus, routine and event-related anti-D may be withheld under the validated local pathway because no D antigen mismatch exists.

Key red flags

Hydrops, abnormal middle cerebral artery peak systolic velocity, fetal tachycardia, reduced fetal movement or ultrasound evidence of anaemia requires urgent fetal-medicine review.

Previous intrauterine transfusion, neonatal exchange transfusion, severe jaundice, stillbirth or an earlier pregnancy affected by HDFN can confer high risk even when the current titre seems modest.

Immune anti-D, anti-c and anti-K are important causes of severe fetal anaemia; anti-K may suppress erythropoiesis without a titre that mirrors disease severity.

Major abdominal trauma, heavy bleeding, fetal death, invasive procedure or another substantial fetomaternal haemorrhage after 20 weeks needs timely anti-D assessment and quantification of fetomaternal haemorrhage.

A transfusion need in a patient with red-cell antibodies requires early transfusion-laboratory involvement because compatible antigen-negative blood may take time to source.

Investigation priorities

ABO and RhD typingFirst step

Define transfusion group and identify RhD-negative pregnancies that may benefit from prophylaxis.

Management branches

Routine preventionPrevent anti-D sensitisation

The pregnant person is RhD negative and no immune anti-D has been identified.

Confirm the booking and 28-week antibody results and consider validated fetal RHD testing where the commissioned pathway offers it.
Administer the licensed local routine regimen at 28 to 30 weeks or at 28 and 34 weeks, documenting product, dose, batch, route and consent.
Continue to assess each sensitising event separately and arrange infant RhD and fetomaternal-haemorrhage testing after birth.

Key medicines

Routine antenatal anti-D immunoglobulinGive intramuscular anti-D using the licensed local regimen: one 1500 IU dose at 28 to 30 weeks or 500 IU at both 28 and 34 weeks.Use only for a non-sensitised RhD-negative patient whose fetus is not known RhD negative; follow the specific product route and SmPC.

Anti-D after a sensitising eventGive the indicated dose within 72 hours; from 20 weeks use at least 500 IU and add further doses according to fetomaternal-haemorrhage testing.Routine antenatal prophylaxis does not cover a later event, and immune anti-D is not treated by giving more immunoglobulin.

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