What Does Being Rh Negative in Pregnancy Mean?

Being Rh negative in pregnancy means your red blood cells do not carry the RhD protein. It does not affect your own health, but if your baby is RhD positive, your body could make antibodies against the baby's blood. Anti-D injections and careful testing are used to prevent this.

Cleveland Clinic notes that about 85 in 100 people are Rh positive. Your blood group and RhD status are checked with a blood test early in pregnancy. The NHS says this is offered at the first antenatal appointment, around 8 to 12 weeks. This guide is for education only; your midwife or doctor will explain what your own results mean.

If you are RhD negative, some events can let a small amount of the baby's blood reach yours. Contact your maternity unit or early pregnancy unit promptly if any of these happen, even if you feel well, because a blood test and extra anti-D may be needed within 72 hours.

Call emergency services (999 in the UK) if you are bleeding and have severe tummy pain, shoulder pain, feel faint or dizzy, or the bleeding is heavy. Later in pregnancy, contact your maternity unit straight away if your baby's movements slow down, change or stop.

• Any vaginal bleeding during pregnancy.
• A fall, accident or blow to your bump.
• Miscarriage, ectopic pregnancy or molar pregnancy.
• Procedures such as amniocentesis, chorionic villus sampling (CVS) or turning a breech baby (external cephalic version).

If an RhD-negative person's blood meets RhD-positive blood, the immune system can learn to make anti-D antibodies. This is called sensitisation. In a later pregnancy with an RhD-positive baby, these antibodies can cross the placenta and break down the baby's red blood cells.

The NHS calls this haemolytic disease of the fetus and newborn (HDFN), also known as rhesus disease. In the baby, it can cause anaemia and jaundice. MedlinePlus explains that a first pregnancy is often not affected because antibodies take time to develop, which is why prevention in every pregnancy protects future ones.

Being RhD negative does not mean your baby will be affected. If your baby is also RhD negative, there is no risk of rhesus disease in that pregnancy.

Anti-D is given as an injection. It helps stop your immune system from making its own anti-D antibodies. Exact schedules and products differ between countries and hospitals, so your team will tell you which applies to you. This guide does not give doses.

In the UK, an NHS hospital guide based on NICE guidance describes a routine antenatal injection at 28 weeks, given between 28 and 30 weeks. Australia's Pregnancy, Birth and Baby describes routine injections at 28 and 34 weeks. In the US, Cleveland Clinic describes Rh immune globulin around 28 weeks if your antibody screen is negative.

• Routine dose in pregnancy: around 28 weeks, following your local schedule.
• After birth: within 72 hours if the baby is confirmed RhD positive.
• After a sensitising event: the NHS hospital guide says within 72 hours; Pregnancy, Birth and Baby says ideally within 72 hours but it can still be given later, so contact your team even if more time has passed.

Alongside your blood group, the early pregnancy blood test checks for red cell antibodies. A negative antibody screen means no relevant antibodies were found, and anti-D is offered to help keep it that way.

If antibodies are already present, the situation is different. The NHS and Cleveland Clinic both say anti-D does not work once your body has made its own antibodies. Instead, you would usually have closer monitoring by a specialist team, who plan care and timing of birth. Ask your team to explain exactly what your result shows.

Yes, in many services. A sample of your blood contains tiny fragments of the baby's DNA, called cell-free fetal DNA (cffDNA). Testing it can predict whether the baby is RhD positive or negative. The NHS hospital guide bases its use on NICE diagnostics guidance.

The NHS hospital guide says the test can be taken from 11+2 weeks and is offered until 25 weeks. Pregnancy, Birth and Baby describes it as more than 99% accurate. If the baby is predicted RhD negative, routine anti-D in pregnancy may not be needed. If the result is RhD positive, inconclusive or you decline the test, routine anti-D is offered.

The test is a prediction, not a final answer. After birth, a sample from the umbilical cord is usually tested to confirm the baby's blood group. Availability varies by country and hospital, so ask whether it is offered where you are.

Having your blood test results with you can make these conversations easier.

• Was my antibody screen negative, and will it be repeated later in pregnancy?
• Is the baby's blood group test (cffDNA) offered here, and when should it be taken?
• When is my routine anti-D due, and where will it be given?
• Who should I call if I have bleeding or a bump injury, and how quickly do I need to be seen?
• If antibodies are found, what monitoring will I have, and who will be looking after me?
• Will the baby's cord blood be tested after birth, and how will I hear the result?

On SameCase, we let patients and verified doctors share de-identified cases and see how similar situations were discussed. Reading about other RhD-negative pregnancies can help you understand terms like antibody screen, sensitising event or cffDNA, and prepare questions for your care team.

Other people's cases cannot predict what will happen in your pregnancy or replace your local schedule. Do not wait to read or post about a case before contacting your maternity team about bleeding, an injury or a missed anti-D appointment.