Managing Rhesus Factor Incompatibility in Pregnancy: What You Need to Know about Rh-sensitivity and WinRho Injection

What is the Rhesus factor?

In Canada, about 85% of people are Rh(+) positive and 15% are Rh(-) negative (Fung & Eason, 2018). You are Rh(-) negative if your red blood cells do not have a protein marker called the ‘rhesus factor’ on them. Rh(+) positive red blood cells do have this protein marker. If your Rh(-) negative blood is exposed to Rh(+) positive blood your immune system will react to this protein by making antibodies to destroy the blood cells carrying it.

What are the dangers of being Rh(-) negative in pregnancy?

If your partner, or the person who provided you with sperm, for this pregnancy, is Rh(-) negative, your baby will also have Rh(-) negative blood and in most cases, nothing further needs to be done. But if your partner is Rh(+) positive, there is a possibility of having an Rh(+) positive baby. This is called rhesus incompatibility.

If you are Rh(-) negative and your baby is Rh(+) positive you have the potential to become ‘sensitized.’ This means that cells in your immune system make antibodies to fight Rh(+) positive blood in the same way they can produce antibodies to fight germs. Most of the time your blood and your baby’s blood do not mix. However, there is about a 12‐16% chance of becoming Rh-sensitized during pregnancy if your baby’s red blood cells mix into your bloodstream (Fung & Eason, 2018). It can take as little as 0.01 mL of blood for sensitization to occur (Fung & Eason, 2018). Certain things put you at a higher risk of becoming sensitized, such as a car accident or other physical injury, invasive genetic testing such as chorionic villus sampling (CVS) or amniocentesis, miscarriage, abortion, turning a breech baby, placental abruption, and giving birth (Fung & Eason, 2018).

What are the risks to my baby if I become Rh-sensitized?

Becoming Rh-sensitized during your first pregnancy is not usually a problem for the baby. But, if you get pregnant again with another Rh(+) positive baby, your immune system can start attacking that baby’s red blood cells, and every other Rh(+) positive fetus you may have. Your Rh(+) positive babies can become very sick, or the pregnancy may not be carried to term (Clarke & Hannon, 2018). If you are already Rh-sensitized, more high-risk obstetrical care is needed.

How Rh-sensitivity develops and how it can impact later pregnancies. Image Copywrite @Britannica

How do I know if I am Rh-sensitized?

A blood test is the only way to check your blood type and find out if you are Rh-sensitized. Your healthcare provider will test your blood during your first appointment to determine your blood type and rhesus factor. If you are Rh(-) negative, you will also be offered a blood test at 28 weeks and again after birth to check for the presence of Rh antibodies.

How is Rh-sensitization in pregnancy prevented?

Rh-sensitization can be prevented with an Rh Immune Globulin injection, called WinRho®.

What is WinRho®?

In Canada, “WinRho®” has been used since 1968 to prevent Rh disease (Soal Therapeutics, 2021). WinRho® is a blood product containing sterile Anti-D Immune Globulin G (IgG) prepared from pooled human red blood cells. WinRho® is mercury, latex, and preservative-free and contains other inactive ingredients including sodium chloride, polysorbate 80, and glycine (Soal Therapeutics, 2021). Typically, WinRho® is injected intramuscularly into your upper arm or buttocks, or intravenously over several minutes.

WinRho injection during pregnancy.

What does WinRho® do?

When your immune system makes antibodies to fight a germ, cells in your immune system ‘remember’ the germ. If you ever come in contact with that germ again, your immune system is ready to fight it. A similar immune response occurs if you are Rh(-) negative and are exposed to Rh(+) positive blood. But, if you receive WinRho® injections, your immune system is ‘fooled’ and does not make antibodies. This protects any Rh(+) positive baby you may have. However, even with a WinRho® injection, the risk of developing antibodies after birth still occurs in 0.04% per 1000 births (Fung & Eason, 2018).

During every pregnancy your doctor or midwife will offer you WinRho®:

• Around 28 weeks of pregnancy

• Within 72 hours after you give birth if your baby is Rh(+) positive

• Following miscarriage, therapeutic abortion, amniocentesis, chorionic villous sampling, or physical trauma (like a car accident or a bad fall while pregnant).

What are the risks of WinRho®?

WinRho® is made from human blood and there is always a small risk of being exposed to viruses that the blood donor may have carried. However, in Canada all blood donors are screened for infectious blood diseases and all Anti-D Immune Globulin G (IgG) is chemically treated and mechanically filtered to kill and remove viruses (Soal Therapeutics, 2021).

What are the possible side effects of getting WinRho?

Most people who receive WinRho® will not experience any side effects, however, possible side effects can include pain and swelling at the injection site, light fever, feeling unwell, headache, and mild allergic reaction. As with any blood product, there is a small risk of a severe allergic reaction that can make it difficult to breathe (anaphylaxis reaction) (Soal Therapeutics, 2021).

Who should not receive WinRho®?

Those who are hypersensitive to human immune globulin or any ingredient in the formulation or component of the injection, have antibodies against IgA and a history of hypersensitivity, have formed anti-D antibodies as confirmed by standard antibody screening tests, or have evidence of autoimmune hemolytic anemia should not receive WinRho® (Soal Therapeutics, 2021).

What happens if I choose not to receive a WinRho®?

Some people are not comfortable receiving any human blood products or you may have other concerns about receiving this injection. Remember, you can decline any intervention as WinRho® is not mandatory. An informed discussion with your healthcare provider about the pros and cons of opting out is encouraged. However, it is important to understand that:

• Without WinRho® there is a 12 to 16% chance that your body will form Rh antibodies (Fung & Eason, 2018).

• If you become pregnant again and are Rh-sensitized, there is a risk that any Rh(+) positive baby will develop Rh disease or Hemolytic Disease of the Fetus and Newborn (HDFN). Rh disease can cause anemia, jaundice or, in some cases, serious problems such as brain damage or even death (Clarke & Hannon, 2018).

• The problems related to Rh disease tend to get worse with each Rh(+) positive pregnancy you have (Clarke & Hannon, 2018).

• There are no effective alternative treatments to prevent Rh disease. An Rh Immune Globulin (WinRho®) injection is the only way to prevent Rh-sensitization (Fung & Eason, 2018).

Parent Resources:

Evidence Based Birth discusses blood types, Rh incompatibility, and WinRho

How Rh factor affects pregnancy.

References:

Clarke, G. & Hannon, J. (2018, July 20). Hemolytic disease of the fetus and newborn. Canadian Blood Services. Retrieved from https://professionaleducation.blood.ca/en/transfusion/clinical-guide/hemolytic-disease-fetus-and-newborn-and-perinatal-immune

Fung, K., & Eason, E. (2018). No. 133-Prevention of Rh alloimmunization. Journal of Obstetrics and Gynaecology Canada, 40(1), e1-e10. Retrieved from https://www.sciencedirect.com/science/article/pii/S1701216317311118

Soal Therapeutics Research Limited. (2021, August 3). WinRho® SDF. Cangene Corporation. Retrieved from https://winrho.com/pdfs/WinRho-PM_EN_3August2021.pdf