Each blood type is also grouped by its Rhesus factor, or Rh factor. A Blood type is either Rh positive (Rh+) or Rh negative (Rh-). Rhesus (Rh) factor is an inherited protein found on the surface of red blood cells. If your blood has the protein, you’re Rh positive (Rh+). If your blood lacks the protein, you’re Rh negative (Rh-). Rh positive is the most common blood type.
The Rh factor is inherited – passed down through parents’ genes to their children. If the mother is Rh negative and the father is Rh positive, the foetus can inherit the Rh gene from the father and could be either Rh positive or Rh negative. If the mother and father are both Rh negative, the baby also will be Rh negative.
“Rh-” and Pregnancy
The Rh factor can cause problems if you are Rh- and your foetus is Rh+. This is called Rh incompatibility. These problems usually do not occur in a first pregnancy, but they can occur in a later pregnancy.
When an Rh-negative mother’s blood comes into contact with blood from her Rh-positive foetus, it causes the Rh-negative mother to make antibodies against the Rh factor. These antibodies attack the Rh factor as if it were a harmful substance. A person with Rh-negative blood who makes Rh antibodies is called “Rh sensitised.”
During pregnancy, the woman and foetus do not share blood systems. However, a small amount of blood from the foetus can cross the placenta into the woman’s system. This sometimes may happen during pregnancy, labour, and birth. It also can occur if an Rh-negative woman has had any of the following during pregnancy:
- Chorionic villus sampling (CVS)
- Bleeding during pregnancy
- Manual rotation of a baby in a breech presentation before labour
- Blunt trauma to the abdomen during pregnancy
During an Rh-negative woman’s first pregnancy with an Rh-positive foetus, serious problems usually do not occur because the baby often is born before the woman’s body develops many antibodies. If preventive treatment is not given during the first pregnancy and the woman later becomes pregnant with an Rh-positive foetus, the baby is at risk of Rh disease.
It also is possible to develop antibodies after a miscarriage, an ectopic pregnancy, or an induced abortion. If an Rh- woman becomes pregnant after one of these events, she does not receive treatment, and the foetus is Rh-, the foetus may be at risk of Rh- related problems.
Problems during pregnancy can occur when Rh antibodies from an Rh-sensitised woman cross the placenta and attack the blood of an Rh-positive foetus. The Rh antibodies destroy some of the foetal red blood cells. This causes haemolytic anaemia, where red blood cells are destroyed faster than the body can replace them.
Red blood cells carry oxygen to all parts of the body. Without enough red blood cells, the foetus will not get enough oxygen. Haemolytic anaemia can lead to serious illness. Severe haemolytic anaemia may even be fatal to the foetus.
A blood test, called an antibody screen, can show if you have developed antibodies to Rh-positive blood and how many antibodies have been made. If you are Rh negative and there is a possibility that your baby is Rh positive, your health care provider may request this test during your first trimester and again during week 28 of pregnancy.
If you are Rh negative, you will be given a shot of Rh immunoglobulin (RhIg). RhIg is made from donated blood. When given to a nonsensitised Rh-negative person, it targets any Rh-positive cells in the bloodstream and prevents the production of Rh antibodies. When given to an Rh-negative woman who has not yet made antibodies against the Rh factor, RhIg can prevent foetal haemolytic anaemia in a later pregnancy. RhIg is not helpful if you are already Rh sensitised.
WHEN IS RHIG GIVEN?
- RhIg is given to Rh-negative women in the following situations:
- At around the 28th week of pregnancy to prevent Rh sensitisation for the rest of the pregnancy
- Within 72 hours after the delivery of an Rh-positive infant
- After a miscarriage, abortion, or ectopic pregnancy
- After amniocentesis or chorionic villus sampling
If you are Rh sensitised, you will be monitored during pregnancy to check the condition of your foetus. If tests show that your baby has severe anaemia, it may be necessary to deliver your baby early (before 37 weeks of pregnancy) or give a blood transfusion while your baby is still in your uterus (through the umbilical cord). If the anemia is mild, your baby may be delivered at the normal time. After delivery, your baby may need a transfusion to replace the blood cells.
Rh- and Miscarriage
It’s normal to want to understand why a miscarriage happened, and it’s frustrating that definitive answers are few and far between. After hearing about the need for RhoGAM (Rho(D) immune globulin) after a miscarriage, many Rh- women wonder whether that blood type might play a role in causing the miscarriages.
The short answer to that is no. Being Rh negative in, and of itself does not cause miscarriage or pregnancy loss. Women who are Rh negative, who have kept up to date with recommended RhoGAM shots and who do not have antibodies against Rh factor do not face increased risk for pregnancy loss due to having Rh negative blood.
Rh- and Stillbirth
Assuming a woman does become sensitised to Rh factor, however, the primary risk is not of pregnancy loss but of Rh incompatibility issues with any future baby to whom she gives birth.
In Rh-negative moms who are sensitised to Rh factor, there’s also an increased risk of stillbirth due to a condition called immune hydrops foetalis that can develop in the second and third trimesters – but this condition is not a factor in first-trimester miscarriages.
The most common cause of first-trimester miscarriages is chromosomal abnormalities in the baby.
If you are Rh negative and concerned that you might be sensitised to Rh factor, talk to your doctor about having a blood test done to check for anti-Rh antibodies. If the test comes back negative, then your Rh status will not bring any increased risks in a future pregnancy (but do continue to get RhoGAM shots per your doctor’s recommendations).
Mothers who are sensitised to Rh factor should be vigilant about seeking prenatal care in any subsequent pregnancy.
While knowing that you’ve tested Rh negative may cause you to worry, especially if you’ve had a miscarriage, remember that miscarriages are incredibly common, and most women who’ve endured them are Rh positive, as is the general population. Moreover, many women who are Rh negative have gone on to have full-term pregnancies and healthy children.
Talk to your doctor about your concerns over your Rh status as well as any other factors that could have potentially led to your pregnancy loss.