A spotlight on plasma: Anti-D Immunoglobulin

Plasma makes up around 55% of blood – it’s what remains after the red blood cells, white blood cells and platelets are removed. Mainly made of water, plasma transports proteins, antibodies and other components around our body, keeping us healthy and providing defence against foreign invaders.

Donations of protein-rich plasma now account for one in seven of all those received by New Zealand Blood Service (NZBS). Often referred to as liquid gold, due to its colour, plasma and plasma-derived products are being put to a wide variety of uses to help save and improve the lives of countless people around New Zealand. One such group are pregnant women who may be at risk of making the Rh antibody called Anti-D. Some people may know it under its older name - RH factor or Rhesus disease factor.

Rh factor

Anti-D is an antibody that binds to red blood cells that carry the RhD blood group. Anti-D is made when the mother has RhD negative blood (she is D negative) and the baby in her womb has RhD positive blood (D positive). When Anti-D is present in a pregnant woman's blood, it will be able to cross the placenta and enter the baby’s blood, causing the baby to start destroying its own red blood cells. If the mother makes only small amounts of Anti-D the baby will be only mildly affected and will be born near the expected day of delivery but is likely to have some health issues such as anaemia and jaundice. Special care will often be needed for the baby after birth.

However, if the mother makes a lot of the antibody the baby will need blood transfusions before birth, just to survive! The transfusions usually need to be repeated every two weeks as the baby grows and needs more blood cells. The baby will also need top-up transfusions after birth because the antibodies will continue to attack the baby’s red blood cells for a few months after birth. Rh disease doesn't harm the mother, but it does affect babies before birth and afterwards.

The problem often starts after the birth of the first baby when some of the baby’s red blood cells enter the mother’s blood during birth. This may cause the mother to start making Anti-D a few weeks or months later– this process is called sensitisation. Unfortunately, once Anti-D production starts it does not stop. During subsequent pregnancies the antibody will start to affect any baby that has inherited the RhD positive blood group from its father. Sometimes, the antibody may even be boosted to higher concentrations if a few of the baby’s red cells escape across the placenta into the mother’s blood during the pregnancy. The baby’s red cells are treated as dangerous because the RhD blood group is very different from RhD negative. Women who have blood group antibodies detected during pregnancy must be monitored closely through most of the pregnancy and especially the last few months to check on the antibody and the baby’s growth and development. Repeated checks are essential so that treatment can be provided for the baby when needed.

Thankfully, Rh disease is uncommon these days because of a plasma product called Anti-D Immunoglobulin, a concentrated solution of Anti-D antibodies.

After pregnancy, and occasionally during pregnancy, around 9% of New Zealand women will need Anti-D Immunoglobulin injections to keep their baby healthy. Every year 7,000 doses of Anti-D are given to RhD negative women.

Anti-D is offered to RhD negative women within 72 hours of the birth of any baby that is RhD positive, or after a bleed or other potentially sensitising event during pregnancy. The dose of antibodies in Anti-D quickly bind to any of the baby’s red blood cells in the mother’s blood stream and cause them to be destroyed. In most cases this will stop the mother from becoming sensitised, subsequently never producing anti-D. Any future babies will then be protected from developing Rh disease in her subsequent pregnancies.

The only way to produce Anti-D is from plasma from blood donors who have already started to make Anti-D. It is donated by a small pool of New Zealanders who have this rare antibody in their blood. Fewer than 0.1% of people in the population have this antibody but only a small number of them are able to donate plasma for the Anti-D Immunoglobulin programme. These extra-special donors help protect many thousands of women and their babies each year. 

To find out more about how you can become a plasma donor, follow this link or call 0800 448 325.

Back to top