Rh Factor Blood Test
Overview
The Rh factor is a protein that can appear on the surface of red blood cells. Blood types are labeled with “Rh-positive” if a person has this protein and “Rh-negative” if they do not. The main blood groups (A, B, AB, and O) can each be either Rh-positive (+) or Rh-negative (–).
| Blood Type Example | Rh Factor Present? |
|---|---|
| A+ | Yes |
| A– | No |
| O+ | Yes |
| O– | No |
Most people are Rh-positive. Fewer people are Rh-negative. This does not cause health problems for most people, but it can be important for pregnant women. It’s a good idea to get a blood test early in pregnancy to check your Rh status.
Purpose of Testing and Treatment
Healthcare providers check Rh factor during pregnancy to protect both the parent and their baby from health problems tied to Rh incompatibility. If a pregnant person is Rh negative and their baby is Rh positive, the immune system could make Rh antibodies if their blood mixes with the baby’s blood.
What Triggers the Need for Testing or Treatment
Blood can mix during certain events like birth, miscarriage, or prenatal tests. These situations raise the risk of sensitization, so healthcare teams monitor Rh antibodies carefully. Common triggers include:
- Delivery
- Abdominal trauma
- Miscarriage or abortion
- Removal of a molar pregnancy
- Ectopic pregnancy
- Amniocentesis
- Chorionic villus sampling
- Cordocentesis
- Bleeding in pregnancy
- Turning a breech-positioned baby manually
If any of these events happen and the parent is Rh negative, medical teams act quickly to lower the risks associated with Rh incompatibility.
The Dangers of Sensitization
If Rh-negative blood is exposed to Rh-positive blood, the immune system may develop antibodies—a process called sensitization. This may not affect the first pregnancy, but future Rh-positive pregnancies can be at risk.
These antibodies may cross the placenta and attack the baby’s red blood cells, causing anemia. Without enough red blood cells to carry oxygen, the baby may need treatment before or after birth, including a transfusion.
How Health Care Teams Respond
Blood tests such as an antibody screen are performed during the first trimester, again at 28 weeks, and after delivery. If no antibodies are found, a shot of Rh immune globulin helps prevent their formation. More doses may be needed after bleeding, miscarriage, or certain tests.
If the baby is Rh-negative, no further treatment is needed. If Rh-positive, an additional shot is given after birth. If sensitization has already occurred, immune globulin will not help. Providers then monitor the baby closely and may treat with in-womb or postnatal transfusions as needed.
Table: Typical Precautions Based on Parent and Baby Rh Status
| Mother’s Rh | Father’s Rh | Possible Baby Rh | Precautions |
|---|---|---|---|
| Positive | Positive | Positive | None |
| Negative | Negative | Negative | None |
| Positive | Negative | Positive/Negative | None |
| Negative | Positive | Positive/Negative | Rh immune globulin injections |
Regular prenatal tests and timely intervention help lower serious risks.
What to Expect During Testing
The Rh factor test is typically done early in pregnancy, often during the first prenatal visit. Here’s what to expect:
- Blood Sample Collection: A small sample of blood is drawn from a vein in your arm. This is a routine process and usually takes just a few minutes.
- No Special Preparation Needed: You don’t need to fast or follow any special instructions before the test. It can be done alongside other early pregnancy blood work.
- Lab Analysis: The blood sample is sent to a laboratory, where it is checked for:
- Rh Factor: Whether your red blood cells have the Rh protein.
- Blood Type: Determines your ABO group (A, B, AB, or O).
- Antibody Screen: Looks for any Rh antibodies that may already be present in your bloodstream.
- Medical History Review: The healthcare provider may also review any history of:
Findings
When a pregnant person with Rh-negative blood carries an Rh-positive baby, their immune system may produce antibodies. This can lead to anemia, hemolytic disease of the newborn, hydrops fetalis, or miscarriage. A preventive Rh immune globulin shot is often given during pregnancy.
Key Preventive Steps:
| Step | Purpose |
|---|---|
| Report any bleeding. | Early detection of antibody production. |
| Rh immune globulin injection. | Prevents antibody development. |
| Remind health team of Rh-negative type. | Ensures correct care during delivery. |
