Red Cell Isoimmunisation (Rhesus Disease)


Although Rhesus disease is uncommon, at the Harris Birthright Centre we treat approximately 50 pregnancies a year that are affected by the condition.

  • What is it?

This is a condition where the mother has antibodies (special proteins) that cross the placenta and attach themselves onto the red blood cells of the baby. The red blood cells are destroyed as a result of this and the baby becomes anaemic. The common type of antibodies are called anti-D and they can only be produced by women who have Rhesus negative blood and are carrying a Rhesus positive baby. The antibodies will only form if the red blood cells of the baby is somehow transferred to the mother's blood. The most likely time for this to happen is when the mother has an invasive procedure during pregnancy or delivery, or if she has bleeding during her pregnancy. 'Anti-D' injections at these times can reduce the chance of antibodies developing and causing Rhesus disease. If antibodies do develop, then any subsequent pregnancies with a Rhesus positive fetus are at risk as the condition is not reversible.

In most cases the condition is not serious because the baby produces new red blood cells to compensate for the ones that are being destroyed. In some cases the cells are being destroyed very quickly. In these cases the baby is unable to produce red blood cells quickly enough and progressively becomes anaemic.

Red blood cells contain haemoglobin, whose function is to pick up oxygen from the placenta and carry it to the various organs of the baby. When the baby becomes anaemic there is not enough haemoglobin to carry oxygen to different parts of the body.

In the early stages of anaemia, the baby tries to compensate for the lack of oxygen. The baby does this by making the heart beat more strongly, so that the blood circulates between the placenta and the baby at a quicker rate. However this process puts strain on the baby's heart and if the anaemia becomes worse then the baby develops heart failure. The first sign of this is a collection of fluid in the baby's abdomen (ascites) and then swelling of skin (oedema). If no treatment is given the baby will die.

  • How will we know the baby is becoming anaemic?
  • Measurement of antibodies in the mother's blood:

A blood sample is taken from the mother, usually every four weeks, to measure the level of antibodies. The amount of antibodies gives an indication of whether the baby is likely to be anaemic. When the level is more than 15 international units (iu/ml) the baby may be anaemic. The only way to know for sure is by taking a fetal blood sample and measuring the fetal haemoglobin.

  • Fetal movements:

Babies that are anaemic move less than usual. Mothers should inform their doctors or midwives if, over a period of a couple of days, the fetal movements are decreased. Again, we will need to measure the fetal haemoglobin by taking a fetal blood sample.

  • Ultrasound scans:

A scan should be performed at 12 and 16 weeks and at regular intervals thereafter. The exact number of scans will be decided by a specialist and will vary according to the severity of the Rhesus disease. An ultrasound scan can easily show if there is excess fluid in the abdomen of the baby. When these features are seen the baby is anaemic and needs to have a transfusion. If there is no extra fluid around the abdomen of the baby a special scan is required (Doppler) to measure how fast the baby's blood is circulating. If the blood flow is faster than normal the baby may be anaemic. In these cases a fetal blood sample needs to be taken to check whether the baby is anaemic or not and confirm that the baby's blood group is Rhesus positive.

  • Fetal blood sampling:

The only way to confirm that the baby is anaemic is by measuring the level of haemoglobin in the baby's blood. The method by which fetal blood is taken is cordocentesis. This procedure carries a risk of miscarriage of 1-2% and therefore will only be performed if there are indications that the baby is becoming anaemic.

During cordocentesis an ultrasound scan is carried out to identify the umbilical cord. A fine needle is then passed through the mother's abdomen and into the umbilical cord. The needle is then used to aspirate blood from the umbilical cord under ultrasound guidance. The sample is then used to measure the level of fetal haemoglobin to confirm that the baby is Rhesus positive. Usually no local anaesthetic is given, but if you are feeling very anxious you have the option of receiving a sedative. It is useful to come to the clinic with your partner or a friend. The procedure takes a few minutes to do and afterwards we check that the fetal heart is beating normally. After each transfusion the fetal heart is monitored for one hour or longer if there is a problem.

  • What will be done following the cordocentesis?
  • When the cordocentesis shows that the baby is not anaemic?

We will check the baby's blood group and if the baby is Rhesus negative, there is no need for further tests and pregnancy will be managed normally. If the baby's blood group is Rhesus positive, you will need to be monitored (for antibody levels, fetal movements and ultrasound) because the baby may still become anaemic. It is important that these tests are carried out one week after the cordocentesis because the baby may become anaemic rapidly. If there are any signs of anaemia, you will need to have the cordocentesis repeated.

  • When the cordocentesis shows that the baby is anaemic?

We will need to give the baby a blood transfusion. In most cases we will need to take blood from you to give to the baby. How many weeks pregnant you are and how anaemic the baby is will determine the amount we have to take. Your blood will need to be 'concentrated' so that it contains mostly red blood cells and this process may take several hours. The procedure of blood transfusion is the same as a cordocentesis, but now the blood is injected into the fetal umbilical cord. Depending on how severe the anaemia is, further blood transfusions are give every one to three weeks.

When your pregnancy reaches 26 weeks we will give you steroid injections that will help your baby's lungs develop, in case the baby is born early. This injection is given every two weeks. We will also recommend that you take iron supplements called Ferrous Sulphate, one tablet three times a day. This will help keep iron levels at a sufficient level, so that you do not become anaemic.

  • What are the chances that my baby will survive?

This will vary from 70% to nearly 100% depending on how severe the Rhesus disease is and on how many transfusions are required. Subsequent growth and development are normal.

  • Where should I have the baby?

When the condition of the baby is good, delivery of the baby is carried out near term and in this case you can have the baby at your hospital. Sometimes the baby may need to be delivered prematurely. In this case it is best that the baby in born in a hospital with special facilities. We have these facilities at King's.

  • Do I need a Caesarean section?

Provided that there are no other problems with your pregnancy you can have a normal delivery. If something goes wrong during a blood transfusion or the baby is very anaemic and or premature, it may be best to carry out a Caesarean section.

  • What will happen after the baby is born?

After the birth the baby will be taken to the neonatal unit to be checked because it may need blood transfusions. Sometimes the baby may have breathing problems and may need to be put on a ventilator.

The management of your Rhesus disease and pregnancy will be discussed with you. A plan of care will be made to meet your individual needs. Please do not hesitate in contacting us if have any further questions.

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