Pregnancy comes with a lot of blood work and testing—and one thing that your doctors are looking for in your blood is your Rh factor. The Rh factor is what determines the “positive” or the “negative” aspect of your blood type, and making sure that your Rh factor and your baby’s are compatible is vital to preventing complications during delivery.
What is Rh Factor?
Blood typing usually involves looking at molecules present on our red blood cells, namely to determine ABO blood type groups (A, B, AB, and O), and rhesus (Rh) factor proteins (positive/negative). Rh factor is inherited from our parents separate from our ABO blood type, and if the protein is present, your blood is considered Rh positive. If the protein is absent, your blood is considered Rh negative.
Your Rh factor status is also vital to know during pregnancy because there’s a possibility that a mom and baby’s blood will be incompatible.
First, it’s important to know that when certain blood types come into contact with each other, they can cause an immune response. Type O blood does not cause a reaction when mixed with other ABO blood types, and Rh-negative blood does not cause a reaction when mixed with either Rh-positive or -negative blood. That’s why individuals with O negative blood are considered “universal donors” (excluding rare blood types, they can donate blood to anyone with any ABO blood types and who are either Rh positive or negative); this is why it’s important to know your blood type before going into surgery or another procedure where you might need a blood transfusion. Your Rh factor status is also vital to know during pregnancy because there’s the possibility that a mom and baby’s blood will be incompatible.
Rh positive is the most common blood type, but having Rh-negative blood does not cause illness or issues by itself and doesn’t typically impact your health. When you are pregnant, however, it’s important to know whether your blood is Rh negative. If your blood is Rh negative and your baby’s blood is Rh negative, there isn’t usually cause for concern, and the same goes for if both your and your baby’s blood are Rh positive. If you are Rh negative and your baby’s blood is Rh positive (a scenario called Rh incompatibility), however, you will need additional care. This is why blood type and Rh factor screening are included in prenatal blood work. If you are Rh negative, your blood work will also include antibody screening.
Rh Factor and Pregnancy
What happens if you are Rh negative and your baby is Rh positive? Typically, your blood doesn’t mix with your baby’s during pregnancy, but it can happen during delivery or other situations like abdominal trauma, bleeding during pregnancy, or miscarriage. If this happens (and you are Rh negative and your baby is Rh positive), your body might start to produce antibodies (an immune response) in reaction to contact with your baby’s red blood cells. While not usually a problem during a first pregnancy, this can cause major issues with subsequent pregnancies if the baby is Rh positive. This is another reason why it’s important to report any bleeding during pregnancy to your provider.
Because your body now recognized an Rh-positive baby as a foreign object (and therefore a theat), your immune system will mount an attack with its antibodies.
Because your body now recognizes an Rh-positive baby as a foreign object (and therefore a threat), your immune system will mount an attack with its antibodies, which cross the placenta and can cause hemolytic anemia, where a baby’s red blood cells are destroyed faster than the baby can create new ones. Hemolytic anemia can be mild to severe. Mild cases might not need treatment, but more severe cases can cause significant problems for the baby, including heart failure, liver failure, jaundice, brain damage, stillbirth, and death after birth.
What does treatment look like?
The good news is that there is treatment for Rh incompatibility. If an Rh-negative mother has not developed antibodies yet, injections of Rh immunoglobulin (RhIg) can prevent her body from producing those antibodies. RhIg injections are often given at 28 weeks and within 72 hours of delivery (delivery is the most likely time when maternal and fetal blood could mix). Every subsequent pregnancy will require additional RhIg treatment. In addition, other times when RhIg treatments might be necessary include:
- An ectopic pregnancy, miscarriage, or abortion
- Certain procedures like amniocentesis, chorionic villi sampling, fetal blood sampling, or fetal surgery
- Blood transfusions
- Removal of a molar pregnancy
- Bleeding during pregnancy
- Abdominal trauma during pregnancy
- External cephalic version procedure (to turn baby from a breech position)
- Accidental needle stick with Rh-positive blood
What happens if you have already developed antibodies?
If you have already developed antibodies, you are considered Rh-sensitized, and RhIg injections are not an effective treatment. In this case, your baby will be monitored regularly by ultrasound. If a baby is growing and developing well, continuing the pregnancy to term may be possible and recommended, though it’s still possible that your baby might need a blood transfusion after birth. If there are indications that your baby has severe hemolytic anemia, an early delivery (before 37 weeks’ gestation) might be considered. In addition, another possible treatment is to give the baby a blood transfusion through their umbilical cord while still in utero.
The good news is that there is a treatment for Rh incompatiblity.
Rh incompatibility can be a scary scenario for moms with Rh-negative blood to face, but blood typing is a regular part of prenatal assessment, and the right care, monitoring, and treatments can help keep your baby (and any future babies) healthy.