A pregnant woman’s blood type can affect how her body builds antibodies that may affect her pregnancy. The most well-known issue is Rh incompatibility – when a pregnant woman with Rh negative blood develops antibodies against the Rh protein on Rh positive fetal red blood cells. This most commonly occurs during the birth of a first Rh positive baby.
Other blood type incompatibilities can also cause problems, though these are much rarer. Understanding a pregnant woman’s blood type and detecting any incompatibility early allows steps to be taken to prevent antibody-mediated pregnancy issues.
What are the different blood types?
There are four main blood types – A, B, AB, and O. These are based on antigens found on the surface of red blood cells. People with type A blood have A antigens, type B have B antigens, type AB have both, and type O have neither.
In addition to these types, blood is either Rh positive or Rh negative. Rh positive blood has the Rh antigen on red blood cells. Rh negative blood does not have this antigen.
So in total there are 8 possible blood types – A+, A-, B+, B-, AB+, AB-, O+, and O-. About 85% of people are Rh positive, and 15% are Rh negative.
Blood type frequencies
The frequency of different blood types varies around the world. In the US population, the most common types are:
| Blood Type | Frequency |
| O+ | 37% |
| A+ | 36% |
| B+ | 9% |
| AB+ | 3% |
| O- | 7% |
| A- | 6% |
| B- | 2% |
| AB- | 1% |
So type O is the most common, followed by type A.
How are blood types inherited?
Blood types are inherited from our parents, following basic Mendelian genetics. The genes that determine blood type are found on chromosome 1.
The A and B antigens are controlled by different versions of the same gene. There are three possible genotypes:
| Genotype | Blood Type |
| IAIA or IAi | A |
| IBIB or IBi | B |
| i | O |
The I codes for the antigen, while the i codes for no antigen. IA and IB are dominant over i. Someone who inherits an A antigen gene (IA or IAi) from one parent and O (i) from the other will be blood type A.
The Rh status is also inherited. Someone who inherits at least one Rh+ gene will be Rh+. If both parents pass on an Rh- gene, the child will be Rh-.
This allows for the many possible combinations of blood types in children from parents of any blood type. For example, parents who are both AO+ could have children with O+, O-, A+, or A- blood types.
How do blood types cause pregnancy problems?
During pregnancy, some mixing of blood can occur between the mother and fetus. This usually does not cause problems. But if the mother’s and baby’s blood are not compatible, the mother’s immune system may detect fetal red blood cells as “foreign” and produce antibodies against them.
The most well known antibody is anti-RhD antibody, produced when an Rh-negative mother is carrying an Rh-positive baby. But antibodies against other blood group antigens can also sometimes occur.
Problems caused by maternal antibodies against fetal blood cells include:
Hemolytic disease of the newborn
This is the main issue caused by Rh incompatibility. It occurs when anti-Rh antibodies cross the placenta and attack fetal Rh+ red blood cells, causing anemia or jaundice after birth. It is preventable through RhIg injections during pregnancy.
Hemolytic disease of the fetus and newborn
Similar to HDN but caused by incompatibility with minor blood antigens other than Rh. This is much rarer but can also have severe effects on the fetus and newborn.
Fetal anemia
Anemia caused by antibody-mediated destruction of fetal red blood cells, leading to hypoxia. This may cause fetal growth restriction, hydrops fetalis (fluid buildup), or stillbirth if severe. It can occur earlier in pregnancy than HDN.
Alloimmune thrombocytopenia
Antibodies destroy fetal platelets, causing platelet deficiency and bleeding risks.
Miscarriage
Severe incompatibility can sometimes lead to antibody-mediated damage severe enough to cause miscarriage, especially in the second trimester. This is uncommon.
So while any pregnancy between mother and baby with incompatible blood types can potentially have issues, Rh incompatibility between an Rh-negative mother and Rh-positive baby is by far the most common and clinically significant. Other blood group incompatibilities usually only cause problems if the mother already has antibodies against those specific antigens.
What are the blood typing issues in pregnancy?
Here is an overview of the most important blood typing pregnancy concerns:
Rh incompatibility
This occurs between an Rh-negative mother and Rh-positive fetus. The most common scenario is an Rh-negative mother giving birth for the first time to an Rh-positive baby. Labor and delivery causes mixing of a small amount of the baby’s blood into the mother’s circulation. Her immune system detects the Rh antigen as foreign and starts producing anti-Rh IgG antibodies.
These antibodies remain in her bloodstream. If she becomes pregnant again with an Rh+ baby, the anti-Rh antibodies can cross the placenta and attack fetal red blood cells. This causes hemolytic disease of the fetus and newborn.
First-time Rh-negative mothers are given a dose of RhIg (RhoGAM) at 28 weeks gestation and again after delivery. This binds any fetal Rh antigen before the mother can become sensitized. It prevents her body from producing anti-Rh antibodies.
If a woman is already Rh-sensitized from a prior pregnancy, the fetus should be closely monitored for anemia with Doppler ultrasound. More intensive treatments like intrauterine blood transfusion may be required. RhIg does not help once a woman is already sensitized.
ABO incompatibility
This is the second most common blood group pregnancy concern, but much less severe than Rh disease. It occurs between blood group O mothers and babies with groups A, B, or AB blood.
Group O mothers may naturally have anti-A or anti-B antibodies even before pregnancy. But these do not cross the placenta well and rarely affect the fetus. ABO issues are usually mild. Babies may have low grade hemolysis at birth causing hyperbilirubinemia and jaundice requiring phototherapy. But this is easily treated.
Minor blood group incompatibility
Incompatibility between more rare blood types like Duffy, Kell, Kidd etc can sometimes cause pregnancy issues. These are uncommon but can potentially be severe.
For example, anti-Kell antibodies are potent and can cause severe fetal anemia. Women may be tested for these antibodies if they have a history problems like unexplained stillbirth or neonatal death. Treatment options are similar to Rh disease.
Bombay phenotype incompatibility
The Bombay blood group is extremely rare, occurring in about 1 in 250,000 people. They have an hh genotype – no A, B, or Rh antigens at all. But they have high levels of anti-A and anti-B antibodies.
If a Bombay phenotype mother carries a baby with a normal blood type like O, A, B, or AB, there is severe incompatibility. Her antibodies will cause potentially lethal HDN or miscarriage. These women face high risk pregnancies and need close monitoring.
How are blood typing issues detected and managed in pregnancy?
Careful monitoring throughout pregnancy is essential to detect and treat blood type incompatibility issues:
Initial blood type screening
All pregnant women have their ABO and Rh blood types tested at the first prenatal visit. This detects those at risk for Rh incompatibility and guides treatment.
Women with prior pregnancy issues may have additional antibody testing to look for anti-Kell, Duffy, etc if other causes are ruled out.
Antibody screening
Women with Rh-negative blood are screened early on for the presence of anti-RhD antibodies. Those found to be Rh-sensitized from a prior pregnancy require close monitoring and treatment.
Women with rare antibodies may need specialized blood products if transfusion is required.
Ultrasound monitoring
Women with known incompatibility issues have serial ultrasounds and Doppler studies to look for signs of fetal anemia like slowed blood flow or fluid buildup. This guides timing of interventions.
RhIg injections
Giving Rh-negative mothers RhIg during pregnancy and after delivery prevents sensitization and protects future pregnancies. This is the standard of care for Rh-negative women.
Intrauterine transfusion
If the fetus develops severe anemia from antibody destruction of blood cells, packed red blood cells can be transfused through the umbilical cord into the fetal circulation under ultrasound guidance. This may be repeated at regular intervals.
Early delivery
If anemia is not treatable by transfusion or the fetus has developed hydrops, early delivery may be induced if the fetus has reached viable gestational age. After birth, the destroy antibodies are removed from circulation. This allows blood cell levels to recover.
Through screening and monitoring of at-risk pregnancies, blood type incompatibility issues can almost always be identified early and treated to prevent serious effects on the baby. Public awareness and standard testing ensures most women with Rh incompatibility receive preventative therapy. For rare blood types, early detection and management of any antibodies present is key to a healthy pregnancy.
What blood types should not get pregnant?
There are no blood types that cannot get pregnant or should absolutely avoid pregnancy. But some combinations face higher risks:
Rh-negative women with Rh-sensitization
Those who already have anti-RhD antibodies from a prior pregnancy face high risks for Rh disease with future Rh-positive babies. But intensive monitoring and intrauterine transfusions allow most to have successful pregnancies. In the rare cases when severe life-threatening anemia cannot be treated before viability, pregnancy termination may be considered.
Bombay blood type women
Without intervention, these women will almost always miscarry or have stillbirth due to blood type incompatibility. It is possible to screen partner’s blood types, perform amniocentesis to determine fetal blood type, and provide intrauterine transfusions. But managing Bombay pregnancies requires frequent invasive testing and procedures. These high risks would reasonably lead some couples to pursue adoption or surrogacy instead. However, Bombay blood type is extremely rare.
Women with rare high-titer antibodies
Women known to have unusually high levels of anti-D, anti-Kell, or other concerning antibodies may be counseled to avoid pregnancy due to high risk. But again, modern medicine can often support a healthy pregnancy with close monitoring.
Overall, there are no blood types considered an absolute contraindication to pregnancy. Almost all women have a good chance of a successful pregnancy with the right medical care. But certain blood combinations face higher risks and challenges. Planning ahead and discussing options with a high risk maternal-fetal medicine specialist allows women to make informed family planning decisions.
What are some tips to prevent blood type pregnancy issues?
Here are some key tips for women to prevent problems from blood type incompatibility during pregnancy:
Know your blood type
Get your blood typed early in life so you know if you are Rh-negative and will require preventative care in pregnancy. Also be aware of any rare types that could impact you.
Get prenatal RhIg injections
All Rh-negative mothers should receive RhIg injections at 28 weeks and after delivery to prevent sensitization. This protects future pregnancies.
Test partner’s blood type
Some couples may consider preconception blood typing of the potential father to determine compatibility with a Bombay phenotype or rare type mother. This allows family planning and counseling before pregnancy.
Follow antibody screening guidelines
Women with high-risk pregnancies should adhere to recommendations for periodic antibody screening and ultrasound monitoring to allow issues like Rh disease to be caught early.
Make delivery hospital choices wisely
For known blood compatibility issues, choose a delivery hospital with expertise in special prenatal treatments like intrauterine transfusions. A pediatric intensive care unit may also be needed.
Seek expert high-risk OB care
Women with identified blood incompatibility problems should partner with a maternal-fetal medicine specialist experienced in their issue. This provides the greatest odds of identifying and managing problems before harm occurs.
While most blood type pairs can have healthy pregnancies, following these basic principles provides the best prevention and prenatal surveillance for at-risk combinations. Under the care of a knowledgeable OB/GYN team, most women can safelycarry and deliver healthy babies despite blood type challenges.
Conclusion
Blood type incompatibility between mother and fetus can cause pregnancy complications like Rh disease and hemolytic issues, but is usually preventable with modern medical care.
Rh incompatibility between Rh-negative mothers and Rh-positive babies is most common. But ABO and other blood antigen mismatches can also sometimes cause problems. Testing and monitoring allow at-risk pregnancies to be identified and any fetal anemia treated with transfusions when needed.
No blood type is completely incompatible with pregnancy. But some women face higher risks that require counseling and planning, like those with Bombay phenotype or previously sensitized Rh-negative mothers. Understanding maternal and fetal blood types remains key to guiding management for a healthy pregnancy and baby.
