Rhesus Disease In Pregnancy

There are a number of conditions which might affect you during childbirth, or indeed the later stages of your pregnancy. These vary in severity, and don’t affect everyone, but disorders like Rhesus Disease can pose serious potential risks to any pregnancy. This article gives you the basic information you might be looking for about Rhesus Disease, why it’s a potential problem during pregnancy, and what you can do to prepare for it.

So what is Rhesus Disease?

While our blood is essentially composed of the same material, there are subtle differences between tiny marker molecules called antigens found in different people. These differences between individuals is the basis of blood typing, where your blood group is given as one of either A, B, AB, or O. Within each of those groups are further subdivisions in positive and negative types, so you might be, for example A+, while a friend might be AB-. These antigens are found on the surface of your blood cells and are inherited from your parents, which is why chances are you share the same blood group as one of your parents at least.

Blood grouping is extremely important in medicine, as administering an incompatible blood type can have dire consequences as the body reacts quite badly to the presence of unrecognised antigens. Antigens are an important part of the mechanism by which our body recognises ‘self’ cells and foreign materials, which is why we have a strong immune reaction to incompatible blood groups.

Apart from the standard blood grouping which is discussed above, there is a further division which can be made based on the presence of the rhesus D antigen (abbreviated to RhD). You can be either RhD positive or negative, depending on whether or not you have this antigen (positive if you do have it, negative if you don’t). Here in the UK an estimated 85% of the population are positive for the rhesus D antigen.

Like blood type, whether you possess the rhesus D antigen or not depends on your parents. We all have two copies of every gene, which determines whether or not we possess a particular trait. If you have one or two copies of the RhD gene you will be rhesus positive, so you do need at least one rhesus positive parent to inherit the antigen.

The presence of the RhD gene and antigen (making you RhD positive) isn’t a disorder of any kind, it’s just a different blood group. The complication of Rhesus Disease actually only occurs during pregnancy, which is why you are likely to first hear about this condition from your midwife or the doctor in charge of your pregnancy.

Rhesus Disease and Pregnancy

Rhesus disease is essentially the complication that occurs when a rhesus D positive baby is born in a rhesus D negative mother. If during the pregnancy or childbirth the RhD negative mother is exposed to rhesus D for the first time, then she will become sensitised to the antigen, which means that she will have an immune response to blood cells from the baby ready to attach those cells upon a second exposure.

During a pregnancy there is a good chance that a baby’s rhesus D positive blood cells can be exposed to maternal rhesus D negative cells. Both mother and unborn child share a common link through the placenta, which is designed to bring maternal and foetal blood into close contact for the exchange of nutrients needed for the pregnancy to continue. An unfortunate effect of this however, is that the placenta also provides a medium through which blood cells can be exchanged, potentially resulting in the Rhesus Disease reaction.

Any bleeding during the pregnancy, for whatever reason, can result in contact between the two incompatible blood types. Similarly abdominal trauma (any injury to the stomach area) or an invasive test like either CVS (chorionic villus sampling) or amniocentesis can create an opportunity for contact between blood cells from mother and child. There is a very high chance of a rhesus reaction occurring during child birth as the blood of both mother and child usually come into contact.

So what happens upon contact between rhesus incompatible maternal and foetal blood is a strong immune reaction, similar to what the body does to deal with any other foreign material like disease causing bacteria and viruses. The mother’s body will begin to produce large amounts of small defensive molecules called antibodies, which are engineered to specifically target the foreign rhesus D antigens on the surface of red blood cells.

Surprisingly enough during the first exposure to RhD positive foetal blood the mother’s body will not be able to generate enough antibodies to actually attack those cells before they are naturally cleared by the body. However, the immune system is designed to respond more quickly upon a second exposure as antibodies specific to RhD have been designed. Which means that if there is further contact between maternal and foetal blood, the baby will develop rhesus disease, which is also why second pregnancies with a RhD positive baby and RhD negative mother bear a much higher risk of rhesus disease.

Rhesus disease itself is where these anti-RhD antibodies from the mother make their way into the baby’s blood, usually by making their way across the placenta after exposure to foetal blood cells. Maternal antibodies like these can stay in the blood stream for up to several months after exposure, during which time the maternal antibodies continue to attack foetal blood cells.

Consequences of rhesus disease

Rhesus disease can ultimately result in a number of different serious complications, depending on the stage of development at which the affected child is. For unborn babies the illness can severely affect the number of working red blood cells circulating in their blood stream, meaning that less oxygen and nutrition is provided to cells that need it in a condition called anaemia. Rhesus disease can also cause foetal heart failure, swelling, or unwanted fluid retention, and can potentially, in the worst of cases, result in a stillbirth (where an unborn child dies shortly before childbirth).

Newborns suffer slightly different effects. Rhesus disease causes the excessive production of a particular compound called bilirubin, which can damage the brain if untreated, causing learning disabilities, deafness, blindness, and in severe cases, death.

There are treatments for these consequences of Rhesus Disease, but as they need to be administered promptly to be effective the safest way forward for you and your baby is prevention. Testing for the presence of the RhD antigen for example, is a good way of finding out whether or not there is a chance of rhesus disease, so that doctors can apply preventative antibodies and avoid any health risks to you or your child.

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