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Blood groups in pregnancy

Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 2 minutes read

Every individual has a different blood type, which is described by the ABO system. There are four main blood types, which have antibodies and antigens. In addition to that, each blood type has another surface antigen, which means they can be either rhesus D positive or rhesus D negative (Rh factor).

This is important to know if, for example, you need a blood transfusion in the case of an operation or an accident. Certain blood types may be incompatible with being transfused with other blood types.

Similarly, it’s very important in pregnancy if a woman is one particular blood type and her unborn baby is another. It can result in severe complications unless treatment is given.

What’s the risk?

If a rhesus-negative mother is pregnant with a rhesus-negative baby, there’s no problem. If the same mother is pregnant with a rhesus-positive baby, this is harmless for the current pregnancy but poses a risk for the second and any future pregnancies. The woman’s immune system sees the rhesus-positive components (antigens) as a threat and responds by producing defending immune components called antibodies.

These will be ready to fight any future pregnancies with rhesus-positive babies, potentially causing harm. This may lead to a condition called rhesus disease of the newborn.

There is no risk if the mother is rhesus positive and she has a rhesus positive or rhesus negative baby.

What is rhesus disease?

In rhesus disease, the antibodies from the mother cross the placenta and attack the red blood cells of the unborn baby. This can continue until shortly before the baby is born. In the womb, this results in anemia in the unborn baby, as the mom's antibodies destroy the baby's red blood cells. Anemia, jaundice (yellowing of the skin due to liver damage), and reduced muscle tone may be evident once the baby is born.

How is it treated?

Anemia in the womb can be detected by ultrasound. It is important to treat rhesus disease immediately, as it can result in stillbirth, brain damage, learning disabilities, and physical disabilities such as blindness. In severe cases, the unborn child may need a transfusion in the womb.

After delivery, the newborn may need admission to the baby intensive care unit to receive a combination of treatments, including blood transfusions, light therapy, and injection of antibodies to prevent further damage. Correct and prompt treatment is effective at preventing further complications.

Can rhesus disease be prevented?

It is very important to attend all your antenatal appointments as scheduled, as you will have your blood tests taken to check your blood group and rhesus status. If a woman is rhesus D negative, she’ll be offered anti-D immunoglobulin injections throughout her pregnancy to remove rhesus D blood cells from the fetus before the woman develops antibodies against them.

If the mother already has anti-D antibodies, then she will be monitored closely throughout pregnancy and delivery, as the injections will be ineffective.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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