Rhesus negative blood and pregnancy: what you need to know

I’ve been told I’m rhesus negative, what does it mean?

The pregnant woman or person is offered a blood test for their blood group (A, B, AB or O) at the antenatal appointment. This blood test also checks for the RhD (rhesus) antigen (NICE, 2021).

• Having the antigen shows rhesus positive (RhD positive) blood.
• Not having the antigen shows rhesus negative (RhD negative) blood.

Both parents pass down blood types to their children. Most people inherit the rhesus [ree-suss] antigen from one or both parents. They will be rhesus negative if they don’t inherit it from either parent (NHS, 2021).

In the UK around 85 in 100 people are rhesus positive, so around 15 in 100 are rhesus negative (NHS, 2021).

What is rhesus disease?

Rhesus disease, or haemolytic disease of the foetus and newborn (HDFN), can cause a baby to have anaemia and jaundice (NHS, 2021).

Rhesus disease only happens when the following three occur together (NHS, 2021):

• the mother or birthing parent has rhesus negative blood
• the unborn baby has rhesus positive blood from their father
• the mother or birthing parent has been exposed to rhesus positive blood in a previous pregnancy

The mother or birthing parent’s pregnant body sees the baby’s rhesus positive blood as an infection and produces antibodies to attack it (NHS, 2021).

If both mother and father are rhesus negative then there won’t be a problem for the baby as they will also be rhesus negative (NHS, 2021).

Rhesus disease is rare, largely preventable, and almost always treatable.

What is sensitisation?

Sensitisation happens when the rhesus negative mother or birthing parent is exposed to rhesus positive blood. This is usually because of a pregnancy with a rhesus positive baby. The antibodies aren’t usually produced quickly enough to affect that baby (NHS, 2021).

However, in the next pregnancy, when the rhesus negative mother or birthing parent is carrying a rhesus positive baby, their body produces antibodies straight away. These cross the placenta and can cause rhesus disease in the baby immediately and for a few months after they are born (NHS, 2021).

Sensitisation can happen at any time during pregnancy. However, it is most common in late pregnancy and during childbirth (McBain et al, 2015).

What causes sensitisation?

Sensitisation during pregnancy is caused by blood cells from the baby crossing into the mother or pregnant person’s blood. This can happen (NHS, 2021; NICE, 2008):

• following an injury to the tummy
• bleeding during the pregnancy
• during Chorionic Villus Sampling (CVS) or amniocentesis – medical interventions where a needle is used to take cells from the placenta or amniotic fluid for testing
• during the birth
• during a miscarriage
• with an ectopic pregnancy

This is why it’s important to give a full history of any previous pregnancies to the midwife and tell them about any bleeding or injury in this pregnancy.

What happens if you’re rhesus negative and pregnant?

If the woman or birthing person is rhesus negative they will be offered one or two injections of Anti-D immunoglobin in pregnancy. Any offer of treatment can be declined.

However, if there has already been sensitisation in a previous pregnancy, the injections do not help. In that situation, the pregnancy and the baby will be monitored more closely (NHS, 2021).

What are anti-D injections?

Anti-D immunogloblin is a medicine which is injected into the mother or birthing person’s muscle. These injections are called Routine Antenatal Anti-D prophylaxis (RAADP). Anti-D removes the baby’s blood cells from the mother or pregnant person’s blood before they can trigger an immune response (NHS, 2021).

Anti-D is made from blood donor plasma. While this is carefully screened, some people have an objection to using blood products (NHS, 2021).

Some women and birthing people have a short reaction to the injection. This could be a rash or flu-like symptoms (NHS, 2021).

The injection is offered at around 28 weeks of pregnancy. Some hospitals offer a second dose at 34 weeks. There is no evidence of difference with one or two doses (NHS, 2021; NICE, 2021).

However, there is evidence that the guidelines are not followed uniformly across the UK. So parents might want to ask questions about the dose used, the number of injections, and the Kleihauer test (NICE, 2008; Wickham, 2024).

The Kleihauer test checks if the mother or birthing person has a higher proportion of the baby’s blood in their system (Wickham, 2024). If it is positive, then it might be advisable to have a repeat dose of Anti-D. You can ask your midwife or doctor about this test as it is not routine.

Anti-D – making a decision

Like any medical offer, Anti-D can be declined. Here are some points to think about:

• Some people prefer not to use blood products, perhaps for religious reasons.
• It isn’t easy to know if someone has become sensitised. This is most likely in the first pregnancy, and the chance reduces with each pregnancy. Once it has happened, it can’t be reversed (Wickham, 2024).
• Postnatal Anti-D is very effective. More good quality evidence is needed about routine antenatal Anti-D (Wickham, 2024).
• In some areas the NHS may not offer Anti-D at a home birth because it requires monitoring they are not able to provide at home (Wickham, 2024). Ask what is available in your local Trust or Board.

Is the unborn baby at risk of rhesus disease?

In a first pregnancy, in most cases there wouldn’t be a problem for the baby. It is unlikely that antibodies would be produced quickly enough to harm the baby (NHS, 2021).

Only in subsequent pregnancies would  rhesus positive babies be affected (NHS, 2021).

If a baby is at risk of rhesus disease, extra monitoring will be offered. This involves measuring the blood flow in the baby’s brain using the same sort of device as that used to listen to the baby’s heartbeat (NHS, 2021).

If the baby was found to have severe rhesus disease it would be treated, and this is usually effective. If they are not treated it could result in brain damage, learning difficulties, hearing loss and blindless or vision loss. Sadly, the baby might also be stillborn (NHS, 2021).

Is it possible to find out if the baby is rhesus positive or negative?

At around 12 weeks of pregnancy, the baby’s blood group can be found by testing the mother or birthing parent’s blood. This can give a reliable result well before the baby is at risk (NHS, 2021).

If the baby has the same rhesus status as the mother or birthing parent, there is no risk of rhesus disease. They will not need extra monitoring or treatment (NHS, 2021).

At birth, if the mother or birthing parent is rhesus negative then blood from the baby’s cord will be tested to see whether they have anti-D antibodies (NHS, 2021).

The test will be offered again in any future pregnancy (NHS, 2021).

What is the treatment for rhesus disease?

Babies in the womb with rhesus disease will be monitored regularly. Around half of all cases of rhesus disease are minor and don’t need much treatment (NHS, 2021).

The baby will be taken to a neonatal unit after birth. In the unit treatment might include (NHS, 2021):

• phototherapy (light therapy)

And in more serious cases:

• blood transfusions
• an injection of antibodies to prevent red blood cells being destroyed

In the most severe cases the baby may need a blood transfusion while they’re in the womb. Some babies may be born early so treatment can start (NHS, 2021).

Signs of rhesus disease in a newborn baby

If the mother or birthing parent is rhesus negative, blood will be taken from the umbilical cord when the baby is born. This checks their blood group and determines if any antibodies have been passed into their blood (NHS, 2021).

Symptoms aren’t always obvious when the baby is born. They can develop up to three months afterwards (NHS, 2021).

The baby might have signs of anaemia such as pale skin, fast breathing or not feeding well. Or they may have jaundice (where the skin of the palms and soles of the feet, and the whites of the eyes appear yellow) (NHS, 2021).