Rhesus Negative Pregnancy: What UK Mums Need to Know
What does rhesus negative mean?
Your blood type combines two systems: ABO (A, B, AB or O) and Rhd factor (positive or negative). If you are rhesus negative - for example O negative or A negative - it means your red blood cells do not have the Rhd marker on their surface. About 15% of people in the UK are rhesus negative. It is not an illness; it is simply a blood type. But in pregnancy it needs careful management.
Why rhesus status matters in pregnancy
If you are rhesus negative and your baby is rhesus positive (inherited from the other parent), some of your baby's red blood cells can enter your circulation. This can happen during birth, but also after bleeding, trauma, miscarriage, certain procedures or antenatal tests.
Your immune system may then treat the baby's Rh-positive cells as foreign and produce anti-D antibodies against them. Once formed, these antibodies persist for life and can attack red blood cells in any future rhesus-positive baby - a condition called haemolytic disease of the newborn (HDN), or rhesus disease.
What rhesus disease can do
Anti-D antibodies cross the placenta and destroy the baby's red cells. Effects can range from mild jaundice after birth to severe anaemia, heart failure or brain damage (kernicterus) in rare cases. Thanks to Anti-D injections, rhesus disease is now very rare in the UK, but monitoring is still important.
How rhesus-negative pregnancy is managed
Blood tests
At your booking visit, your blood is checked for blood group, Rh factor and any pre-existing antibodies. Antibody screening is repeated at 28 weeks to catch any that have developed during pregnancy.
Anti-D injections
These prevent your immune system from making anti-D antibodies. They are offered:
- Routine: one dose at around 28 weeks of pregnancy
- After potential sensitising events: bleeding, abdominal trauma, miscarriage, ectopic pregnancy, amniocentesis or external cephalic version
- After birth: if your baby is confirmed to be rhesus positive
Read our page on Anti-D injections in pregnancy for detailed information.
Potential sensitising events
Tell your midwife straight away if you have:
- Vaginal bleeding during pregnancy
- Abdominal trauma (e.g. a fall or car accident)
- A miscarriage or ectopic pregnancy
- An invasive procedure such as amniocentesis or CVS
- External cephalic version (turning a breech baby)
Each of these may trigger a dose of Anti-D within 72 hours.
What if antibodies develop?
If your antibody screen is positive, you will be referred to a specialist. Depending on the type and level of antibody, you may have:
- Regular ultrasound scans to check blood flow in the baby's brain (middle cerebral artery Doppler), which indicates anaemia
- Blood tests to measure antibody levels
- In rare cases, intrauterine transfusion or early delivery
Most rhesus-negative women never develop antibodies thanks to Anti-D.
Can I find out my baby's blood type before birth?
In some UK centres, a test called non-invasive prenatal testing (NIPT) for fetal RhD can be performed from about 10-12 weeks using a blood sample from you. If the baby is confirmed rhesus negative, routine Anti-D is not needed. This is becoming more widely available on the NHS.
Practical tips
Being rhesus negative sounds frightening, but with modern Anti-D prophylaxis, serious problems are very rare. Attend your appointments, report any bleeding promptly and ask questions - your midwife is there to guide you through every step.