Anti-D Immunoglobulin (RhoGAM)
Updated May 2026
Editorial position
Anti-D immunoglobulin prophylaxis is one of the most successful preventive interventions in antenatal care, reducing Rh sensitisation rates from 10-20 percent in the pre-prophylaxis era to under 1 percent today. This page summarises the dose, timing, and evidence drawing on NICE TA156 and ACOG guidance. It is not personal medical advice. Decisions about anti-D administration are made with your antenatal team.
The clinical problem anti-D solves
About 15 percent of European-origin women are Rh-D negative. If a Rh-negative woman becomes pregnant by a Rh-positive partner, the baby has a chance of being Rh-positive. Fetal red cells can cross the placenta in small numbers throughout pregnancy and in much larger numbers at delivery. If the mother's immune system encounters Rh-positive red cells, it can produce anti-D antibodies (sensitisation).
Sensitisation does not affect the current pregnancy in most cases, because the antibody response takes weeks to develop and the exposure peak is at delivery. The risk is to subsequent pregnancies. In a future pregnancy with a Rh-positive baby, the pre-formed anti-D crosses the placenta efficiently (it is IgG class) and can attack the fetal red cells, causing severe anaemia, hydrops fetalis, and intrauterine death.
Before anti-D prophylaxis was introduced in the late 1960s, Rh haemolytic disease of the newborn was a major cause of perinatal death and disability. The rate of Rh sensitisation in untreated Rh-negative women carrying Rh-positive babies was 10 to 20 percent per pregnancy, accumulating across reproductive life. Modern anti-D prophylaxis has reduced sensitisation to under 1 percent.
How anti-D prevents sensitisation
Anti-D immunoglobulin given to a Rh-negative mother binds to any fetal Rh-positive red cells in her circulation, marking them for clearance by the spleen before her own immune system can mount a response. The mechanism is essentially passive immunoprophylaxis: the imported anti-D does the work the mother's own immune system would otherwise do, but without leaving a memory.
The dose required depends on the size of the fetal-maternal haemorrhage. A standard 500 IU UK or 300 mcg US dose protects against approximately 4 to 6 mL of fetal red cells. After delivery, the Kleihauer-Betke test or flow cytometry assay quantifies fetal-maternal haemorrhage; if it is larger than the standard dose covers, additional anti-D is given to match.
Anti-D is sourced from human plasma donors who have been deliberately immunised to produce anti-D antibodies. The manufacturing process includes virus inactivation (solvent-detergent and other steps) to eliminate bloodborne virus risk. The product has a strong safety record across decades of use.
The routine antenatal dose
Both the UK (NICE TA156) and the US (ACOG) recommend routine antenatal anti-D at around 28 weeks of pregnancy for all non-sensitised Rh-negative women whose baby is, or might be, Rh-positive. The 28-week dose covers the second half of pregnancy, when small spontaneous fetal-maternal haemorrhages are most common.
Two regimens are in use in the UK: a single dose at 28 weeks (most common) and a two-dose regimen at 28 and 34 weeks. Both are clinically equivalent in trials. The choice often comes down to local commissioning and product availability. The standard single dose is 1500 IU in the UK; the standard two-dose regimen uses smaller doses.
US practice typically uses one or two 300 mcg doses at 28 weeks (and sometimes 32 weeks). The dose units differ between countries (mcg vs IU) but the underlying anti-D quantity is comparable.
The postnatal dose
If the baby is confirmed Rh-positive at delivery, the mother receives a postnatal anti-D dose within 72 hours. Cord blood is tested at delivery for ABO and Rh-D. The postnatal dose covers the larger fetal-maternal haemorrhage that typically occurs at delivery.
Standard postnatal dose is 500 IU (UK) or 300 mcg (US), with additional doses if fetal-maternal haemorrhage testing shows larger-than-expected red cell transfer. Caesarean section, manual removal of the placenta, abruption, traumatic delivery, and twin pregnancies all increase the chance of larger haemorrhage and may prompt FMH testing.
If the baby is confirmed Rh-negative at delivery (cord blood typing), the postnatal anti-D dose is not needed.
Sensitising events during pregnancy
Several events during pregnancy can cause fetal-maternal haemorrhage and warrant additional anti-D doses for Rh-negative women: miscarriage (after 12 weeks generally; some practice gives anti-D for earlier miscarriage too), ectopic pregnancy, antepartum bleeding, abdominal trauma (including motor vehicle collisions), external cephalic version (turning a breech baby at term), and invasive procedures such as amniocentesis and chorionic villus sampling.
UK doses for sensitising events are 250 IU before 20 weeks of pregnancy and 500 IU from 20 weeks onwards. US doses are 50 mcg (mini-dose) before 12 weeks, with a full 300 mcg dose from 12 weeks. The mini-dose is appropriate for early pregnancy where total fetal red cell volume is small.
For any sensitising event after 20 weeks, fetal-maternal haemorrhage testing (Kleihauer-Betke or flow cytometry) helps determine if additional anti-D is needed beyond the standard sensitising-event dose.
NIPT-RhD: tailoring anti-D to need
About 35 to 40 percent of Rh-negative pregnant women are carrying a Rh-negative baby and do not need routine anti-D prophylaxis. Cell-free fetal DNA in maternal blood can identify the fetal Rh-D genotype from about 11 to 13 weeks of pregnancy onwards. The UK NHS rolled out routine NIPT-RhD for Rh-negative women in 2021 following the 2017 NICE DG25 cost-effectiveness analysis.
For Rh-negative women carrying a confirmed Rh-negative baby (as determined by NIPT-RhD), routine antenatal and postnatal anti-D are not needed. This avoids unnecessary administration of a blood-product-derived medicine, conserves anti-D supply, and reduces the small risks of any injection.
The US has not adopted routine NIPT-RhD on the same scale. Anti-D prophylaxis remains universal for eligible women in US practice. Some private practices offer NIPT-RhD on individual request. The cost-benefit calculation differs between UK universal screening and US insurance-based pathways.
If a dose is missed
Missing a routine antenatal dose increases the risk of sensitisation but does not eliminate the protection from a postnatal dose. The postnatal dose given within 72 hours of delivery still provides substantial protection if given on time.
Late postnatal anti-D (administered up to 9 to 10 days after delivery) provides declining but still useful protection. Anti-D administered more than 13 days postpartum is unlikely to prevent sensitisation that has already occurred. In any case where a dose has been missed, the antenatal team should be informed promptly so that the appropriate next step can be planned.
The maternal antibody screen at the next pregnancy will detect any sensitisation that has occurred. If sensitisation is detected, future pregnancies are managed by a fetal medicine team with serial monitoring and intrauterine transfusion if needed.
Frequently asked questions
What is anti-D immunoglobulin?
When is the routine antenatal anti-D dose given?
When is the postnatal anti-D dose given?
When are sensitising-event anti-D doses given?
Do I need anti-D if my baby will be Rh-negative?
What happens if I miss the antenatal anti-D dose?
Is anti-D immunoglobulin safe?
Talk to your antenatal team
All decisions about anti-D administration are made with your midwife or obstetrician. This page is general information, not personal advice. UK: contact your maternity unit or call NHS 111 for urgent advice. US: contact your obstetric provider. For emergencies anywhere, call 999 or 911.