About rhesus negative blood type and pregnancy
There are two different types of rhesus blood types: rhesus positive and rhesus negative. Fifteen percent of all Danes are rhesus negative, the rest are rhesus positive. When you are pregnant it is important you know your blood type as special precautions apply for women who are rhesus negative.
You have had a blood sample taken by your general practitioner that has shown that you are rhesus negative. The baby’s blood type will also need to be determined via a blood sample taken from you at around the 25th week of pregnancy. If your baby is also rhesus negative, no more steps need to be taken. On the other hand, if your baby is rhesus positive, we recommend that you are treated to prevent rhesus sensitisation.
Preventing rhesus sensitisation
Injections with anti-D immunoglobulin
Rhesus sensitisation means that your body will begin producing antibodies to your baby's blood. If you are rhesus negative and your baby is rhesus positive, you will be offered two injections of anti-D to stop your body from producing antibodies.
The injections contain a substance called anti-D immunoglobulin. All pregnant women who are rhesus negative and who are expecting a baby that is rhesus positive will be offered two injections: one injection around the 29th week of pregnancy and one injection after delivery. Injection can also be given later in pregnancy, e.g. if the baby needs to be moved out of a breeched position.
The anti-D is injected into a muscle in either your thigh or hip. After the injection you will need to wait about 20 minutes before you can go home to ensure you do not have an allergic reaction, e.g. itching or difficulty breathing.
The injection is harmless for the baby.
About rhesus sensitisation
Without injections of anti-D, your body might begin producing antibodies to your baby’s blood cells because the baby has a D-factor on its blood cells that you do not because you are rhesus negative. D-factor is a protein found only in the rhesus positive blood type. It is the D-factor that you might begin producing antibodies to.
You will only begin producing antibodies if the baby’s blood enters your bloodstream, for example when you are giving birth, after a miscarriage or if you bleed in pregnancy for any reason. When a rhesus negative mother gives birth to a rhesus positive baby, some of the baby's blood will almost always enter the mother's bloodstream during delivery. In most cases, this will cause rhesus sensitisation. Rhesus sensitisation is therefore seldom a problem during the first pregnancy but can be an issue during a subsequent pregnancy if you do not receive preventative anti-D injections.
Without preventive injections you will produce antibodies that during a future pregnancy can cross the placenta and attack the baby’s red blood cells. In rare cases this can cause the baby to develop anaemia while in the uterus. We can usually treat the anaemia, but sometimes delivery will have to be induced prior to the due date to keep the anaemia from developing.
Things to be aware of
You will be given a card
Anti-D immunoglobulin can be detected in your blood for a period of 6 months. This can affect you if you need a vaccination or a blood transfusion. You will therefore be given a vaccination card stating that you have received anti-D injection. Store the card together with your health card (sundhedskort) and show it when you have an appointment at your general practitioner or at the hospital.
Future pregnancies
Anti-D immunoglobulin will gradually disappear from your body. This means that you will need another injection of anti-D immunoglobulin in connection with a new pregnancy if the baby is rhesus positive.