If you are Rh-negative, your red blood cells do not have a marker called Rh factor on them. Rh-positive blood does have this marker. If your blood mixes with Rh-positive blood, your immune system will react to the Rh factor by making antibodies to destroy it. This immune system response is called Rh sensitization.
Rh sensitization can occur during pregnancy if you are Rh-negative and pregnant with a developing baby (fetus) who has Rh-positive blood. In most cases, your blood will not mix with your baby's blood until delivery. It takes a while to make antibodies that can affect the baby, so during your first pregnancy, the baby probably would not be affected.
But if you get pregnant again with an Rh-positive baby, the antibodies already in your blood could attack the baby's red blood cells. This can cause the baby to have anemia, jaundice, or more serious problems. This is called Rh disease. The problems will tend to get worse with each Rh-positive pregnancy you have.
Rh sensitization is one reason it's important to see your doctor in the first trimester of pregnancy. It doesn't cause any warning symptoms, and a blood test is the only way to know you have it or are at risk for it.
Rh sensitization during pregnancy can only happen if a woman has Rh-negative blood and only if her baby has Rh-positive blood.
If you have Rh-negative blood, your doctor will probably treat you as though the baby's blood is Rh-positive no matter what the father's blood type is, just to be on the safe side.
All pregnant women get a blood test at their first prenatal visit during early pregnancy. This test will show if you have Rh-negative blood and if you are Rh-sensitized.
If you have Rh-negative blood but are not sensitized:
If you are Rh-sensitized, your doctor will watch your pregnancy carefully. You may have:
If you have Rh-negative blood but are not Rh-sensitized, your doctor will give you one or more shots of Rh immune globulin (such as RhoGAM). This prevents Rh sensitization in nearly all women who use it.
You may get a shot of Rh immune globulin:
The shots only work for a short time, so you will need to repeat this treatment each time you get pregnant. (To prevent sensitization in future pregnancies, Rh immune globulin is also given when an Rh-negative woman has a miscarriage, abortion, or ectopic pregnancy.)
The shots won't work if you are already Rh-sensitized.
If you are Rh-sensitized, you will have regular testing to see how your baby is doing. You may also need to see a doctor who specializes in high-risk pregnancies (a perinatologist).
Treatment of the baby is based on how severe the loss of red blood cells (anemia) is.
In the past, Rh sensitization was often deadly for the baby. But improved testing and treatment mean that now most babies with Rh disease survive and do well after birth.
Rh sensitization can occur when a person with Rh-negative blood is exposed to Rh-positive blood. Most women who become sensitized do so during childbirth, when their blood mixes with the Rh-positive blood of their fetus. After being exposed, a mother's immune system produces antibodies against Rh-positive red blood cells.
The minimum amount of blood mixing that causes sensitization is not known. Fortunately, Rh sensitization can almost always be prevented with the Rh immune globulin injection.
When an Rh-negative person's immune system is first exposed to Rh-positive blood, it takes several weeks to develop immunoglobulin M, or IgM, antibodies. IgM antibodies are too large to cross the placenta. So the Rh-positive fetus that first triggers maternal sensitization is usually not harmed.
A previously Rh-sensitized immune system rapidly reacts to Rh-positive blood, as during a second pregnancy with an Rh-positive fetus. Usually within hours of Rh-positive blood exposure, smaller immunoglobulin G, or IgG, antibodies are formed. IgG antibodies can cross the placenta and destroy fetal red blood cells. This causes Rh disease, which is dangerous for the fetus.
Some Rh-negative people never become sensitized, even after exposure to large amounts of Rh-positive blood. The reason for this is not known.
If you are already Rh-sensitized or become Rh-sensitized while pregnant, you will not have any unusual symptoms.
Fetal problems from Rh sensitization are detected with Doppler ultrasound testing and sometimes with amniocentesis. It is possible, though, that a fetus with severe Rh disease will move less frequently than it did earlier in the pregnancy.
Other conditions with symptoms similar to Rh sensitization include other blood type incompatibility problems and fetal infections.
Unless you are given Rh immune globulin just before or after a high-risk event, such as miscarriage, amniocentesis, abortion, ectopic pregnancy, or childbirth, you have a chance of becoming sensitized to an Rh-positive fetus's blood.
If you have been Rh-sensitized in the past, you must be closely watched during any pregnancy with an Rh-positive partner, because your fetus is more likely to have Rh-positive blood. In response to an Rh-positive fetus, your immune system may quickly develop IgG antibodies, which can cross the placenta and destroy fetal red blood cells. Each subsequent pregnancy with an Rh-positive fetus may produce more serious problems for the fetus. The resulting fetal disease (called Rh disease, hemolytic disease of the newborn, or erythroblastosis fetalis) can be mild to severe.
If you have been Rh-sensitized in the past, an Rh-negative fetus cannot trigger an immune reaction.
Rh sensitization can occur when a person with Rh-negative blood is exposed to Rh-positive blood. During pregnancy, an Rh-negative woman can become sensitized if she is carrying an Rh-positive fetus.
Things that increase the risk of blood mixing and sensitization during pregnancy include:
Although rare, Rh sensitization has been known to occur after needle sharing between intravenous drug users. Transfusing Rh-positive blood in an Rh-negative person can also trigger sensitization. But this is extremely rare, because blood is always tested prior to transfusion.
Your pregnancy will be closely watched. Discuss possible symptoms early in pregnancy with your doctor. You'll need repeated tests to watch the fetus.
Call your doctor now if you note a decrease in your fetus's movement after 24 to 26 weeks of pregnancy.
Call your doctor now if you:
If you are pregnant, you will have your first prenatal tests during your first trimester. Every woman has her blood tested at the first prenatal visit to see what her blood type is. If your blood is Rh-negative, it will also be tested for antibodies to Rh-positive blood. If you have antibodies, that means that you have been sensitized to Rh-positive blood. The antibodies can now kill Rh-positive red blood cells.
If you are Rh-negative and your partner is Rh-positive, your fetus is likely to be Rh-positive.
If you are pregnant or have miscarried, or if you have had an elective abortion, a partial molar pregnancy, or an ectopic pregnancy, you will need testing to see if you have been sensitized to Rh-positive blood.
All pregnant women have an indirect Coombs test during early pregnancy.
If you are already Rh-sensitized or become sensitized while pregnant, close monitoring is important to determine whether your fetus is being harmed.
If your blood is Rh-negative and you have been sensitized to Rh-positive blood, you now have antibodies to Rh-positive blood. The antibodies kill Rh-positive red blood cells. If you become pregnant with an Rh-positive baby (fetus), the antibodies can destroy your fetus's red blood cells. This can cause anemia.
If you are already Rh-sensitized and are pregnant, your treatment will focus on preventing or minimizing fetal harm and on avoiding early (preterm) delivery.
Treatment options depend on how well or poorly the fetus is doing.
If you are an Rh-negative woman and you have conceived with an Rh-negative partner, you are not at risk of Rh sensitization during pregnancy. (Most health professionals treat all Rh-negative pregnant women as though the father might be Rh-positive.)
If you are already sensitized to the Rh factor, your pregnancy will need to be closely monitored to prevent fetal harm. For more information on fetal and newborn treatment, see Treatment Overview.
If you are unsensitized Rh-negative, treatment focuses on preventing Rh sensitization during pregnancy and childbirth. Rh immune globulin (such as RhoGAM) is a highly effective treatment for preventing sensitization.
Rh immune globulin is also needed within 72 hours after vaginal bleeding, a miscarriage, partial molar pregnancy, ectopic pregnancy, or abortion.
Use of Rh immune globulin is effective in preventing Rh sensitization. Rh immune globulin contains Rh antibodies that have been purified from human donors. This treatment prevents an unsensitized Rh-negative mother from making antibodies against her fetus's Rh-positive blood.
If an affected fetus younger than 34 weeks needs to be delivered, corticosteroid medicine (betamethasone or dexamethasone) may be given to the mother to speed fetal lung development before a premature birth.
Other Works Consulted
- American College of Obstetrics and Gynecologists (2017). Prevention of Rh D alloimmunization. ACOG Practice Bulletin No. 181. Obstetrics and Gynecology, 130(2): e57–e70. DOI: 10.1097/AOG.0000000000002232. Accessed July 9, 2018.
- Moise KJ Jr (2008). Management of rhesus alloimmunization in pregnancy. Obstetrics and Gynecology, 112(1): 164–176.
- Roman AS (2013). Late pregnancy complications. In AH DeCherney et al., eds., Current Diagnosis and Treatment Obstetrics & Gynecology, 11th ed., pp. 250–266. New York: McGraw-Hill.
- U.S. Preventive Services Task Force (2004). Screening for Rh (D) incompatibility. Rockville, MD: Agency for Healthcare Research and Quality. Available online: http://www.uspreventiveservicestaskforce.org/uspstf/uspsdrhi.htm
Current as of: October 8, 2020
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