Negative Blood Types (A-, B-, AB-, O-)
Why do midwives need to know my blood type?
The natural process of birth always involves some amount of bleeding, even in low risk pregnancies. As such, for your safety, it is important for your midwife to know your blood type. Determining blood type is one of the first tests run at the beginning of pregnancy, as part of the initial routine blood work.
In addition, your midwife will look specifically at if you have a Rh positive (A+, B+, AB+, O+) or Rh negative (A-, B-, AB-, O-) blood type. Rh factor is a marker present with positive blood types and NOT present with negative blood types. Rh factor has no impact on general health. However, during pregnancy, if Rh negative blood (no Rh factor) is exposed to Rh positive blood (Rh factor present), the immune system reacts to the Rh factor by making antibodies to destroy the blood cells carrying it.
What does this mean for my pregnancy and baby?
Approximately 15% of the Canadian population is Rh-negative (ORBCon, 2017). Clients who are Rh-negative are at risk of becoming sensitized to Rh-positive blood if the baby they are carrying is Rh-positive. Sensitization occurs when your immune system makes antibodies to attack the Rh-positive blood that has entered your blood system. Normally, your blood and your baby’s blood do not mix. However, some events put Rh negative clients at higher risk for sensitization, including:
- Physical trauma (car accident or bad fall)
- Invasive genetic testing (Chorionic villus sampling or amniocentesis)
- Turning a breech baby (ECV)
- Placental abruption
- Giving birth
For the majority of clients, becoming sensitized in the first pregnancy does not cause any complications for the baby. Complications are more likely to arise during subsequent pregnancies with Rh positive babies. The client’s body retains the antibodies produced during the first sensitizing event (usually birth), triggering the immune system to attack the Rh positive red blood cells of a subsequent Rh positive baby. This fetus or baby is then at risk for developing a condition called hemolytic disease of the fetus and newborn. Hemolytic disease of the fetus and newborn can cause complications including anemia, jaundice, or potentially brain damage or death.
How to prevent hemolytic disease of the fetus and newborn
To prevent hemolytic disease of the fetus and newborn, the goal is to prevent Rh sensitization of the client in the first place. This is done using Rh Immune Globulin (called WinRho or Rhogam). Rh Immune Globulin is a human blood product containing Rh antibodies and administered through intramuscular injection. When your body is allowed to make its own antibodies the immune system will be triggered to produce these same antibodies in a future circumstance. When you are given an injection of WinRho, the body does not produce its own antibodies. The WinRho Rh antibodies do not stay in your blood system forever. Thus, during the next pregnancy with an Rh positive baby, your body won’t recognize the Rh positive blood and will not produce antibodies. Therefore, preventing hemolytic disease of the fetus and newborn. The injection of Rh Immune Globulin is 99.9% effective in preventing Rh sensitization (ORBCon, 2017).
When do I receive the injection of Rh Immune Globulin?
Your blood type will be known after your initial blood work and will be tested again between 24-28 weeks. Additionally, if you are Rh-negative, you will be offered a blood test after birth to check for Rh antibodies. For all Rh negative clients, your midwife will offer you a shot of Rh Immune Globulin (WinRho) in the following circumstances:
- At 28 weeks of pregnancy
- Within 72 hours after birth, if your baby is confirmed to be Rh positive
- Following a miscarriage, therapeutic abortion, amniocentesis, chorionic villous sampling and trauma event (car accident or bad fall)
The vast majority of clients who receive Rh Immune Globulin (WinRho) at these recommended intervals, go on to have uncomplicated pregnancies and healthy babies. Please consult the resources below or ask your midwife for additional information.