Rhesus Negative and Anti-D

What being RhD negative means

The RhD factor is a protein on the surface of red blood cells. ACOG's patient information puts it simply: "If your blood cells have this protein, you are Rh positive. If your blood cells do not have this protein, you are Rh negative."

Being RhD negative is not a problem in itself. It only matters if your baby is RhD positive and some of the baby's blood reaches your bloodstream. ACOG describes what follows: "her body will recognize that the Rh-positive blood is not hers. Her body will try to destroy it by making anti-Rh antibodies."

The NHS names the condition those antibodies can cause: haemolytic disease of the fetus and newborn, or HDFN, "a rare blood disorder where your immune system attacks your baby's blood cells. It's sometimes called rhesus disease."

The crucial detail is the timing. ACOG: "Health problems usually do not occur during an Rh-negative woman's first pregnancy with an Rh-positive fetus. This is because her body does not have a chance to develop a lot of antibodies." The risk is to later pregnancies — which is why the whole system is built around prevention rather than treatment.

How you find out

Through the routine booking blood test. The NHS says HDFN "is routinely screened for during pregnancy. You'll be offered a blood test at your first antenatal appointment at 8 to 12 weeks." If your blood type is D positive there is no risk of HDFN; if it is D negative, your baby's blood type is tested too.

In Ireland, the HSE describes the same booking test for blood group and rhesus status, and notes that "some hospitals can check if your baby is rhesus negative. If your baby is rhesus negative, you do not need anti-D injections."

That last point is a real change in practice. NICE has assessed high-throughput non-invasive prenatal testing for fetal RHD genotype — originally published as diagnostics guidance DG25 and now carried forward as HealthTech guidance HTG420 — which uses cell-free fetal DNA in your blood to work out the baby's RhD type, so that anti-D can be targeted to the people who actually need it. Whether it is available to you depends on your service.

When anti-D is given

Anti-D immunoglobulin works by mopping up any of the baby's RhD-positive cells before your immune system can react to them. ACOG describes it as "a medication that stops the body from making Rh antibodies if it has not already made them", and adds the limitation: "It is not helpful if your body has already made Rh antibodies."

Routine antenatal prophylaxis. In the UK, NICE technology appraisal TA156 recommends routine antenatal anti-D prophylaxis "as a treatment option for all pregnant women who are rhesus D (RhD) negative and who are not known to be sensitised to the RhD antigen." In Ireland, the HSE says anti-D may be offered at 28 weeks, after your baby's birth, and early in pregnancy if you have an injury to your tummy or a bleed. In the US, ACOG describes anti-D given at 28 weeks of pregnancy and within 72 hours after the delivery of an Rh-positive baby, noting that "each pregnancy and delivery of an Rh-positive baby requires a repeat dose."

After events during pregnancy. ACOG lists a dose as recommended after a miscarriage or abortion at 12 weeks or more; after an ectopic pregnancy, amniocentesis, chorionic villus sampling, fetal blood sampling or fetal surgery; after bleeding beyond 20 weeks; after abdominal trauma; and after attempts to turn a baby from breech.

What changed in the UK in 2026

NICE updated its early pregnancy anti-D recommendations in June 2026, and the new thresholds are gestation-specific and quite firm.

• NICE recommendation 1.18.1: "Do not offer anti-D immunoglobulin prophylaxis... for an ectopic pregnancy, miscarriage or threatened miscarriage up to and including 11+6 weeks' gestation." If ultrasound dating and last menstrual period disagree, NICE says use the ultrasound.
• Recommendation 1.18.2: offer anti-D at a dose of at least 250 IU (50 micrograms) to people who are RhD negative and at 12+0 to 12+6 completed weeks who are having medical management or a surgical procedure for an ectopic pregnancy or miscarriage.
• Recommendation 1.18.3: consider anti-D at at least 250 IU (50 micrograms) at 12+0 to 12+6 weeks for threatened miscarriage with heavy or recurrent bleeding.
• Recommendation 1.18.5: "Do not use a Kleihauer test for quantifying feto-maternal haemorrhage" in this context.

If you were given anti-D after an early loss in a previous pregnancy and are not offered it this time, that is why. It is a deliberate change, not an oversight — though it is entirely reasonable to ask your clinician to confirm your dating and explain the decision.

Note that these dose figures are the UK's. ACOG's patient guidance frames the US position around a 12-week line too, and says that if you are less than 12 weeks pregnant at the time of a miscarriage or abortion, you should "talk with your ob-gyn about whether RhIg is right for you." Doses and products differ between countries, so quote the body, not just the number.

What anti-D is made of

NICE tells clinicians to cover this explicitly: anti-D "is a protein obtained from blood plasma, but... it does not contain blood cells (it is a filtered blood product)." The HSE says the injection "is safe for you and your baby." If you have a religious or personal objection to blood products, raise it early rather than at the point of the injection, so alternatives and consequences can be discussed properly.

If antibodies have already formed

Anti-D cannot undo sensitisation. ACOG: "RhIg treatment does not help if an Rh-negative woman has already made antibodies. In this case, the well-being of the fetus will be checked during the pregnancy, usually with ultrasound exams."

The NHS describes what care then looks like: extra scans and blood tests to monitor the baby during pregnancy, and monitoring for jaundice and anaemia after birth. Treatment during pregnancy can include blood transfusions for the baby and weekly immunoglobulin treatments for you; after birth it can include light therapy for jaundice or an exchange blood transfusion. The NHS adds that "the risk of complications is low because the treatments are usually very effective."

What to actually do

• Know your blood group, and check it is written in your notes.
• If you are RhD negative, tell any clinician who sees you for bleeding, abdominal trauma or an invasive test — including in an emergency department, where it may not be obvious from your records.
• If you bleed after 12 weeks, mention your blood group when you phone. It changes what happens next.
• If you have already had anti-D this pregnancy, keep a note of the date. Further doses may still be needed after separate events.

Urgent advice applies to the bleeding, not the blood group. Heavy vaginal bleeding, severe abdominal pain, shoulder-tip pain, dizziness or fainting means calling your maternity unit, early pregnancy service or your local emergency number now — 999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, 111 in New Zealand. Being RhD negative does not change that threshold.