Rh Factor
and the Anti D injection

Having a Negative Rh Factor in pregnancy puts you into a special category. If your midwife or doctor tests your blood and tells you that you have a Rh D Negative blood type, you will be given more information about Anti-D prophylaxis.

For non-pregnant people being blood group Negative Rh Factor is not an issue at all, in fact it only becomes of interest if you need a blood transfusion.

But in pregnancy if you are one of the 16% of people who have the Rhesus Negative blood type then there are a few issues to cover.

Why is RH factor important in pregnancy?

The baby growing inside you may inherit its blood group and Rh factor from its mother or its father.

So a baby may be either Rhesus positive or negative depending on the mother and father’s blood type.

If the father of the baby is Rhesus Positive and its mother is Rhesus Negative, baby may inherit either blood type. Around 10% of births are Rhesus Positive babies born to Rhesus Negative mothers.

For most Rhesus Negative mothers there is little cause for concern. However sometimes blood sensitisation happens, when baby’s blood mixes with its mother’s blood. This is most likely to happen after some kind of haemorrhage, after an invasive test like amniocentisis, or during the labour and childbirth event. It can also happen during miscarriage, abortion or as a result of some trauma to the mother's abdomen.

It is not common thankfully, but if feto-maternal haemorrhage does happen the mother’s Rhesus Negative blood can become sensitised.

This is a reaction called isoimmunisation. The mother’s body believes the baby’s blood cells are an abnormal antigen and then antibodies are created.

The sensitization reaction in the mother’s blood is life-long. Although your baby is unlikely to suffer any harm in the current pregnancy, once sensitized, the mother will make antibodies against any baby with a Rhesus Positive blood type in any future pregnancy.

This means that any future baby that is Rh Factor D Positive may suffer with a serious and sometimes fatal illness in the form of haemolytic disease of the newborn.

midwife taking blood test

Will I need Anti D injections in pregnancy?

To help protect mothers and babies from this problem a blood group and Rhesus factor type is diagnosed by a blood test, early in the pregnancy, usually at your booking appointment.

If a Rhesus Negative blood type is detected you will be offered protection with an immunoglobulin injection in the form of Anti-D which is generally given at a routine appointment around your 28th week of pregnancy.

Anti-D is an injection carefully manufactured from human blood derivatives. The dose is adjusted and the injection issued by your local maternity hospital blood transfusion laboratory.

Ideally Anti-D should also be offered to all Rhesus Negative women within 72 hours after any suspected sensitization event, such as a fall or vaginal bleed during pregnancy, or after invasive screening tests or external cephalic version. It should also be given after birth, abortion or miscarriage.

The mother’s blood should be tested at anytime if sensitization is suspected.

As a prophylactic measure, an Anti-D injection is now recommended at 28 weeks of pregnancy for all Rhesus Negative women to help prevent sensitisation.

injection of Anti D

Immediately after the birth, Rhesus Negative mothers will have a small sample of blood taken, along with a small sample from the umbilical cord of her newborn baby. These two blood samples are sent for analysis. The hospital laboratory will check if sensitization is occurring, and will also identify if the baby is Rhesus Positive or Negative.

Depending on these results, an Anti-D injection should be given to a Rh Negative mother within 72 hours from birth where the baby is identified as having a Rh Positive blood type.

Routine administration of Anti-D reduces the risk of maternal antibodies developing and therefore protects future babies from the potentially devastating results of haemolytic disease.

Anti-D immunoglobulin has been used for nearly 50 years and has not shown to have any major adverse reactions. However as a precaution it is usually administered at a hospital clinic just in case any adverse reaction should occur.

If you have a Rh Positive Blood type you will not need anti-d injections.

Read more about Haemolytic Disease


Rh Factor - to Antenatal Care
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