Pregnancy and Rhesus factor

Rhesus factor is a substance found in people’s blood. Everybody’s blood is either rhesus positive or rhesus negative.

On its own the rhesus factor does not cause health problems. But when a mother is Rh negative and her fetus is Rh positive, there can be health risks for that fetus and for the fetus of any subsequent pregnancies she may have.

If a pregnant woman with Rh-negative blood is pregnant with a baby (fetus) with Rh-positive blood, Rh sensitization may occur. The baby may have Rh-positive blood if the father has Rh-positive blood. Rh sensitization happens when the baby’s blood mixes with the mother’s blood during pregnancy or delivery. This causes the mother’s immune system to make antibodies against the baby’s red blood cells in future pregnancies. This antibody response is called Rh sensitization and, depending on when it happens, can destroy the red blood cells of the baby before or after it is born. If sensitization happens, a fetus or newborn can develop mild to severe problems (called Rh disease orerythroblastosis fetalis). In rare cases, if Rh disease is not treated, the fetus or newborn may die.

Here it goes with some more details:

1. If the mother is Rh negative and the father is Rh positive, their fetus may be Rh positive or Rh negative.

2. If the fetus is Rh positive, there is a risk that some of its Rh positive blood cells will get into the mother’s bloodstream during the pregnancy or delivery and mix with her Rh negative blood.

3. Left untreated, the mother’s blood will make antibodies that attack the Rh positive blood of the fetus.

4. These antibodies can cause health problems for the fetus, such as anaemia or even death.

5. If the mother then has another baby later on that is also Rh positive, her antibodies may cross the placenta and attack the baby’s blood, destroying its blood cells.

The chance of forming Rh antibodies occurs with each pregnancy, including ectopic pregnancies (when the fertilised egg implants itself outside the uterus) and pregnancies that end in miscarriage or termination.

Fortunatly, a woman with Rh-negative blood can get a shot of Rh immunoglobulin that almost always stops sensitization from occurring. Problems from Rh sensitization have become very rare since Rh immunoglobulin was developed. This injection is known as anti-D and contains anti-D gammaglobulin.

Anti-D is given to Rh negative mothers who have given birth to an Rh positive baby. The injection is usually given within a few hours of giving birth. Anti-D should prevent rhesus antibodies forming, which would affect any further pregnancies the mother has.

To prevent early sensitisation, anti-D is also given to Rh negative women at 28 weeks of pregnancy and again at 34 weeks.

Earlier or additional doses of anti-D are also generally given if there is an episode of vaginal bleeding during the pregnancy, and when invasive tests such as amniocentesis or chorionic villus sampling are performed. Women who have a miscarriage, an ectopic pregnancy or a termination of pregnancy will also need anti-D, even if it is the first pregnancy, to protect future pregnancies. These are all situations where fetal blood may mix with the mother’s blood causing Rh antibodies to form.

Anti-D should be given within 72 hours of the immune system coming into contact with blood from the fetus. It is too late to give the injection if rhesus antibodies have already formed.

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