So why is this important?
When people receive blood transfusions, they are given blood matching their blood type. Otherwise the person can develop blood antibodies, proteins designed to protect the body. Antibodies develop when a foreign antigen or protein enters the body. (The body sees viruses and bacteria as foreign proteins.)
Since the blood type of an unborn baby is partly determined by the father’s blood type, it may not be the same as that of the mother. During pregnancy, the baby’s blood is normally kept separate from the mother’s. Very few blood cells cross the placenta, where nutrients, oxygen and waste are transferred between mother and baby. If the mother is Rh-negative and the baby is Rh-positive and the bloods of mother and baby mix, the mother can develop antibodies to the baby’s blood.
If the mother develops antibodies to the baby’s blood type, those antibodies can cross the placenta and attack the baby’s blood cells. This is called Rh incompatibility and can cause severe anemia or stillbirth. After birth, a yellow pigment called bilirubin can build up in the baby’s blood causing jaundice, nerve damage to the baby’s vision, hearing and touch, heart problems, decreased muscle tone or mental handicaps. The mother herself is in no danger. Rh incompatibility only happens if the mother is Rh-negative while her baby is Rh-positive.
It does not happen if the mother is Rh-positive and the baby is Rh-negative.
A woman with Rh-negative blood has nothing to worry about if her baby is also Rh-negative, and a woman with Rh-positive blood need not worry at all. However, other antibodies unrelated to the Rh type can cause hemolytic diseases in newborns.
Since mixing of blood doesn’t usually happen until delivery, Rh incompatibility will not usually affect the woman’s first Rh-positive child. Still, a few Rh-negative women (about two per cent) somehow develop antibodies to their baby’s Rh-positive blood during their last three months of pregnancy. Giving the mother a special blood product called Rho(D) immune globulin (RHIG) at about 26 to 28 weeks into the pregnancy can usually prevent the problem.
Other situations where mother’s and baby’s blood is likely to mix include amniocentesis, during a miscarriage, abortion or an ectopic pregnancy (a pregnancy in the fallopian tube), after injury to the abdomen, or if there is heavy bleeding during the pregnancy.
If the mother-to-be is Rh-negative, the father’s blood type may be tested. If his blood type is negative, the baby cannot carry the Rh antigen from either parent and must be Rh-negative too. However, since not all mothers are absolutely certain who the father of the baby is, most prenatal caregivers assume that the father’s blood type is Rh-positive.
If an Rh-negative woman has received a blood transfusion containing Rh-positive red cells, she may develop Rh antibodies that can cause problems if she becomes pregnant.To prevent this from happening, it is now routine to give an Rh-negative transfusion to an Rh-negative woman who requires a transfusion and may become pregnant in the future.
How do we stop Rh disease from happening?
During the first prenatal visit, every pregnant woman is asked to have blood tests which can determine her blood type and search for antibodies to various blood antigens. If the woman is Rh-negative, she is warned that in a situation where her blood and the baby’s are likely to mix, she will need to receive Rho(D) immune globulin within 72 hours. She will also receive Rho(D) immune globulin at 28 weeks of pregnancy and again after delivery if her child is Rh-positive.
Rho(D) immune globulin contains Rh antibodies made from human plasma (one of the substances in blood). It stops the mother’s immune (defence) system from making antibodies to the baby’s blood. The Rho(D) immune globulin antibodies destroy any of the baby’s blood cells entering the mother’s blood before the mother’s own immune system has time to react to them.
What are the side effects of Rho(D) immune globulin?
The most common side effects of receiving Rho(D) immune globulin include swelling or redness at the site of the injection or a slight fever. Since Rho(D) immune globulin is made from human blood (plasma), there is a chance someone receiving it may develop an infection. Since human plasma is screened for HIV and hepatitis and the Rho(D) immune globulin is treated to destroy viruses, this risk is very, very small.
Still, the Rho(D) immune globulin treatment is not always effective. A small number of women produce antibodies even after receiving the injection, so a larger dose of RHIG has to be given. The risk of significant Rho(D) immune globulin side effects is small, only about one in 60,000 injections.
How can a mother-to-be tell whether she has developed Rh antibodies?
The mother will not have any warning symptoms to suggest that she and her baby have developed Rh disease.The only way to tell for certain is through blood tests.
What is the risk of developing Rh disease?
If the baby is Rh-positive and the mother Rh-negative, there is about a 15 per cent chance that the mother will produce antibodies to the baby’s blood if she does not receive the recommended treatment.
What if a baby does develop Rh disease?
If the mother is Rh-negative, her blood will be tested at least twice during the pregnancy for Rh antibodies. If antibodies are found, retesting will be done monthly to monitor the amount of antibodies present. If the amount increases, the condition of the baby’s red blood cells may be tested in one of two ways. The fluid around the baby can be tested using amniocentesis. Alternatively, in percutaneous umbilical blood sampling (PUBS) a blood sample can be drawn from a vein in the umbilical cord. Both procedures involve drawing samples through the mother’s abdomen.
Depending on how severely the disease affects the baby, a transfusion may be needed after birth to replace diseased Rh-positive red blood cells and remove the yellow bilirubin pigment. A very sick baby may be delivered early or given transfusions through the umbilical cord before birth. The survival rate for babies who receive a transfusion while in the womb (where the baby grows) is as high as 80 to 100 per cent. Some babies with Rh disease develop a condition called hydrops, caused by severe anemia. Babies with hydrops also require transfusions, but the chances of survival are only about 40 to 70 per cent.
In most cases, Rh disease can be prevented by using Rho(D) immune globulin. Once the mother’s own antibodies have developed, they last forever. The mother produces more antibodies with each pregnancy, so the risk of Rh disease gets worse each time. By receiving early prenatal care, a woman can protect her unborn baby and any future pregnancies.