Pregnancy from two parents with incompatible blood types, can it lead to complications?

Let's take Alice and Bob, both healthy adult human specimens. Alice is (A-). Bob is (B+).

If they decide to have a child, would Alice's pregnancy involve any additional risk or complications compared with, say, Abraham and Abigail's pregnancy (both AB+)?


I overheard claims that pregnancies from parents with different blood groups can lead to complications in pregnancy due to interactions between the mother and the child's blood. (These claims were not officially backed, otherwise I would have brought them up on Skeptics.SE). The explanations and my Google browsing went beyond my biology knowledge. I know these pregnancies must be viable, since the AB group exists, but I do not know if there are edge cases that lead to complications that would not happen with same blood type parents.

Related question

Can the mating of a couple with Rhesus positive and negative blood types result in miscarriage? This question only asks about Rh+ and only if it leads to miscarriage.

The rhesus factor (the + / - part of the blood group) can cause complications with pregnancy under certain conditions and lead to the so called Rh disease:

If the mother is rhesus negative and the father, rhesus positive; then the birth of a child with Rh+ blood group (inherited from the father) can cause the mother to build antibodies against this blood group. Therefore, a second pregnancy with a child that also has Rh+ blood group can have complications if no precautions are taken at any other point.

If these specific conditions are not all met, then no complications should arise from the blood groups.

The only complications that will occur will be in the birth of the second child, and that too if the second child is conceived soon after the birth of the first.

Let me explain.

Rh factor is an antigenic protein found on the surface of the RBCs of some individuals( rather, 'most individuals').

If the factor is present, the blood group is written with a positive(+) sign, and if it is absent, the negative sign(-) is used with the blood group. Therefore, in your example, Bob, Abraham and Abigail have the said factor on their RBCs whereas Alice does not.

As a matter of fact, our body has a mechanism because of which it produces antibodies against foreign antigens. Antibodies are simply substances released by our specialized cells to counter toxins and foreign antigens. These antibodies bind with the specific antigens (against which they are released) to render them harmless.

The fact is that these antibodies, once produced in our bodies, remain in the bloodstream for a certain interval of time, and there presence protects us from future infections by those antigens(This is the principle exploited in vaccination).

Let us relate this knowledge of antibodies and antigens to the Rh factor. Let's say that we make a blood transfusion from an Rh positive person(like Bob) to an Rh negative person( like Alice). Since for Alice, the Rh antigen is a foreign antigen(because it is naturally absent from her blood), she will get sensitized and develop antibodies against it. However, these antibodies will not attack the antigens immediately. They will come into action only if the antigens are again brought into the bloodstream, i.e. another transfusion is made sometime later. These antibodies will then bind to the RBCs carrying it, and result in agglutination, or clumping of RBCs. The clump of RBCs thus formed blocks the passage of blood to the heart, resulting in death.

So, if Alice and Bob conceive a child together for the first time, the fetus will be Rh positive(because if the factor is present in any one parent, it will also be found in the child), and it will sensitize the blood of the mother. At this point, if you know some basics of biology, you will think that since the blood of the mother and the fetus never comes in contact, the fetal blood should not be able to sensitize the mother's blood. If you think so, you are absolutely right! The placenta does not allow their blood to mix. However during the parturition, rupturing of placenta often occurs, causing just a small amount of the fetal blood to mix with that of the mother. Even this small amount is enough for the mother to be sensitized and develop antibodies against Rh factor.

Now, if the second child(who will also,obviously, be Rh positive) is conceived soon, there will be a problem. The placenta is permeable to antibodies, and as a result, the anibodies developed earlier will enter the fetus and cause agglutination in the fetal blood, leading to excessive anaemia or even death. This is called erythroblastosis fetalis, or hemolytic disease of the newborn(HDN)

Thus, you can see that Alice and Bob will have a problem with their 2nd child, whereas Abigail and Abraham will not, since they are both Rh positive and Abigail won't be sensitized.

FACT The Rh factor was first found, and named after, the common Rhesus monkey!!

When a Baby's Blood Type Doesn't Match His Mom's

Vincent Iannelli, MD, is a board-certified pediatrician and fellow of the American Academy of Pediatrics. Dr. Iannelli has cared for children for more than 20 years.

Lyndsey Garbi, MD, is a pediatrician who is double board-certified in pediatrics and neonatology.

After waiting nine long months to meet their baby, little could be more delightful for proud new parents than taking stock of whose ears he got, whose dimpled chin, whose extraordinarily long and slender toes. But what about his blood type? While it may be just fine that an infant's hair color, say, is different than his mom's (even if she was secretly hoping he'd inherit her strawberry blond curls), it sometimes is a different story if an infant's blood type isn't the same as his mother's. In that case, he could be at risk for a condition known as ABO blood type incompatibility, a type of illness known as a hemolytic disease of the newborn (HDN).   (Another example of an HDN occurs when a mother's blood is Rh-negative and her baby is Rh-positive. Rh factor incompatibility is screened for during pregnancy an expectant mom can be given a shot to deflect problems.)  

In the past, an HDN (clinically known as erythroblastosis fetalis) could put a baby's health at serious risk. In fact, at one time HDNs were a major cause of death for new babies. Now that medical researchers better understand the mechanisms that cause HDNs, they aren't nearly as threatening. If you're a new mom whose baby's blood type is different from yours, here's what you need to know about ABO incompatibility.

Rh Factor Blood Type and Pregnancy

Usually your Rh factor blood type isn’t an issue. But during pregnancy, being Rh-negative can be a problem if your baby is Rh-positive. If your blood and your baby’s blood mix, your body will start to make antibodies that can damage your baby’s red blood cells. This could cause your baby to develop anemia and other problems.

Each person’s blood is one of four major types: A, B, AB, or O. Blood types are determined by the types of antigens on the blood cells. Antigens are proteins on the surface of blood cells that can cause a response from the immune system. The Rh factor is a type of protein on the surface of red blood cells. Most people who have the Rh factor are Rh-positive and those who do not are Rh-negative.

How do I know if I am Rh negative or Rh positive?

As part of your prenatal care, you will have blood tests to find out your blood type. If your blood lacks the Rh antigen, it is called Rh-negative. If it has the antigen, it is called Rh-positive. When the mother is Rh-negative and the father is Rh-positive, the fetus can inherit the Rh factor from the father. This makes the fetus Rh-positive too.

Problems can arise when the fetus’s blood has the Rh factor and the mother’s blood does not. You may develop antibodies to an Rh-positive baby. If a small amount of the baby’s blood mixes with your blood, which often happens, your body may respond as if it were allergic to the baby. Your body may make antibodies to the Rh antigens in the baby’s blood. This means you have become sensitized and your antibodies can cross the placenta and attack your baby’s blood.

They break down the fetus’s red blood cells and produce anemia (a condition that happens when the blood has a low number of red blood cells). This condition is called hemolytic disease or hemolytic anemia. It can become severe enough to cause serious illness, brain damage, or even death in the fetus or newborn. Sensitization can occur any time the fetus’s blood mixes with the mother’s blood.

It can occur if an Rh-negative woman has had:

How can problems be prevented?

  • A blood test can provide you with your blood type and Rh factor.
  • Antibody screen is another blood test that can show if an Rh-negative woman has developed antibodies to Rh-positive blood.
  • An injection of Rh immunoglobulin (RhIg), a blood product that can prevent sensitization of an Rh-negative mother.

RhIg is used during pregnancy and after delivery:

  • If a woman with Rh-negative blood has not been sensitized, her doctor may suggest she receive RhIg around the 28th week of pregnancy to prevent sensitization for the rest of pregnancy.
  • If the baby is born with Rh-positive blood, the mother should be given another dose of RhIg to prevent her from making antibodies to the Rh-positive cells she may have received from their baby before and during delivery.
  • The treatment of RhIg is only good for the pregnancy in which it is given. Each pregnancy and delivery of an Rh-positive child requires repeat doses of RhIg.
  • Rh-negative women should also receive treatment after any miscarriage, ectopic pregnancy, or induced abortion to prevent any chance of the woman developing antibodies that would attack a future Rh-positive baby.

What are some other reasons RhIg may be given?

  • If and when amniocentesis is conducted, fetal Rh-positive red blood cells can mix with a mother’s Rh-negative blood. This would cause her to produce antibodies, therefore making it necessary for RhIg to be given.

A Rh-negative mother may receive RhIg after birth, even if she decides to have her fallopian tubes tied and cut to prevent future pregnancies for the following reasons:

  1. The woman may decide later to try to have the sterilization reversed.
  2. There is a slight chance the sterilization may fail to prevent pregnancy.
  3. In case there is a need for a blood transfusion in the future, the treatment will prevent her from developing antibodies.

What happens if antibodies develop?

Once a woman develops antibodies, RhIg treatment does not help. A mother who is Rh sensitized will be checked during her pregnancy to see if the fetus is developing the condition. The baby may be delivered on time, followed by a blood transfusion for the baby that will replace the diseased blood cells with healthy blood. For more severe cases, the baby may be delivered early or given transfusions while in the mother’s uterus.

How common is the Rh-negative factor?

  • More than 85% of people are Rh-positive.
  • The Rh factor does not affect a person’s general health.
  • Problems can occur during pregnancy when the baby’s blood has the Rh factor and the mother’s blood does not, however it can be prevented in most cases with the medication called immunoglobulin (RhIg).

Get the Fetal Life App for Apple and Android endorsed by the American Pregnancy Association. It features meal recommendations, kicks counter, blood glucose tracking, and more.

Compiled using information from the following sources:

1. Mayo Clinic Complete Book of Pregnancy & Babys First Year. Johnson, Robert V., M.D., et al, Ch. 11.

2. Danforths Obstetrics and Gynecology Ninth Ed. Scott, James R., et al, Ch. 18.

What is the rarest blood type?

The rarest blood type is Rhnull. Unlike other blood types, people with Rhnull blood have no antigens on their red blood cells.

Researchers estimate that just 1 in 6 million people have Rhnull blood.

Healthcare professionals classify blood type according to the presence or absence of antigens, which are proteins attached to red blood cells.

In this article, learn more about the rarest blood type. We also cover other blood types, including whether or not they are compatible with each other.

Share on Pinterest Rhnull is the rarest blood type.

The American Red Cross define a blood type as “rare” when it occurs in fewer than 1 in 1,000 people. Rhnull is the rarest of these.

Having a rare blood type can make it difficult or even impossible to get a blood transfusion or organ transplant.

It can also cause other health issues. For example, if their blood is incompatible with a developing fetus, pregnant women with rare blood types may experience complications. One Iranian woman with Rhnull blood had several pregnancy losses.

Most blood types fall into one of four blood type groups, according to whether they contain A or B antigens.

For example, people with A antigens have type A blood, while those with B antigens have type B blood. People with both A and B antigens have type AB blood, while people with neither antigen on their red blood cells have type O blood.

In addition to the blood group type, a person may also carry Rh factor on their red blood cells. A person without Rh factor has Rh- blood, while someone with it has Rh+ blood. For example, a person with AB blood and Rh factor has AB+ blood.

Some people, including those with Rhnull blood, lack one or more common antigens. There are more than 30 other known blood groups and more than 600 antigens .

Although most people have blood that falls into one of four blood group types, these types vary in prevalence across ethnic groups and geographic regions.

According to data from the Stanford School of Medicine Blood Center, AB- blood is the rarest type in the United States. Just 0.6% of people in the U.S. have this blood type.

The prevalence of the other common blood types in the U.S. is as follows:

  • O+: 37.4%
  • O-: 6.6%
  • A+: 35.7%
  • A-: 6.3%
  • B+: 8.5%
  • B-: 1.5%
  • AB+: 3.4%
  • AB-: 0.6%

Blood type prevalence varies across populations and geographic regions.

Researchers once sought to classify people into distinct races based upon blood groups, but blood types do not fit into racial categories.

Across geographic regions, O blood groups are the most common. In fact, around 63% of the world’s population has this blood group.

In Central and South America, the rate of O blood is much higher — close to 100% in some regions. In Eastern Europe and Central Asia, the rate of O blood is lower, and B blood is more common.

That being said, B blood is the least common group across the globe. Only around 16% of the world’s population has it.

Across the world, Rh+ blood is much more common than Rh- blood. The lowest known rate of Rh+ blood is still high, at around 65% among the Basque people of the Pyrenees mountains. Sub-Saharan African populations have the highest rate of Rh+ blood, at around 97–99%.

Blood type is a genetic trait. However, a child can have a different blood type to both of their parents, depending on which genes they inherit.

Each parent passes one allele (gene) for blood type to their child. A parent who has O blood can only pass an O allele.

A and B alleles are “co-dominant.” This means that a child who inherits one of each will have AB blood.

For example, a mother with type A blood who passes on an A allele and a father with type B blood who passes on the B allele will have a child with AB blood.

Parents pass on Rh factor in the same way. Rh+ blood is dominant. This means that if a child inherits one Rh+ allele and one Rh- allele, the child will have Rh+ blood. To be Rh-, the child must inherit two Rh- alleles. This is because it is recessive.

In 2015, researchers identified an enzyme that could “cut” antigens from blood cells. In theory, this would allow doctors to change a person’s blood type, potentially making it easier for them to get a transfusion.

However, the researchers had to use very large quantities of the enzyme, and they did not test their theory in human participants. Although it might one day be possible, doctors cannot currently change a person’s blood type.

A person can only give blood to someone with compatible blood antigens.

People with Rh- blood can give blood to both Rh- and Rh+ recipients. However, those with Rh+ blood cannot give to Rh- recipients.

If a person receives blood from someone with an incompatible blood type, it can cause a life threatening immune system reaction. The blood transfusion will likely fail.

A person with type O blood can donate to anyone, as long as the Rh factor is compatible. This means that people with O+ blood can donate to someone with A+, AB+, B+, or O+ blood, but not to people with O-, B-, AB-, or A- blood.

O- is a universal donor, which means that a person with this blood type can donate to anyone.

A person with type AB blood is a universal recipient, as long as the Rh factor is compatible. This means that they can receive blood from all other blood groups.

People with group AB, A, or B blood can only donate to people with the same blood group type.

Having a rare blood type makes it more difficult for a person to receive a blood transfusion. It can also increase the risk of certain health complications, especially following an organ transplant and during pregnancy.

People who are curious about their blood type can ask a doctor for a quick blood test. Many people learn their blood type when they donate blood for the first time.

People with rare blood types should ask a doctor about access to safe blood transfusions.

How Does Blood Type Influence Fertility and Pregnancy?

We’re still learning about how blood type may impact fertility and pregnancy, but here’s what some of the research shows:

  • Type Os and Egg Quality: A study conducted by researchers from the Albert Einstein College of Medicine found that women in their 30s with blood type O who were struggling to conceive were twice as likely to have elevated FSH (follicle stimulating hormone) levels as women with type A blood. (Note: Elevated FSH is just one sign of declining egg health. So, consider learning more about FSH Levels and Fertility.)
  • Type Os and Immune Response: Some fertility specialists speculate that type Os have an imbalanced immune reaction that could affect implantation, especially in IVF treatments. This could, in part, account for poorer IVF outcomes in women with type O blood.
  • A-B-O Incompatibility: While many couples with different blood types have no problem conceiving, in a small number of cases it may pose a problem. A-B-O incompatibility occurs when the mother is type O and the baby is A or B (from the father). A research review published in the International Journal of Molecular and Cellular Medicine suggests that A-B-O incompatibility occurs in around 20% of pregnancies. Of those, only 20% are affected by thius, which can lead to newborn jaundice or possible miscarriage.
  • Rh Factor: Rh factor is one of the blood groups’ subtypes. A person is either Rh positive or negative. Rh disease in newborns can occur if the baby is Rh positive and the mother is Rh negative. In these cases, the mother’s immune system reacts and passes on antibodies to the baby (usually during a second pregnancy) that lead to anemia or jaundice. A simple blood test during pregnancy can reveal whether your baby is at risk. Receiving preventive treatment with immune globulins (Rh shot) in early pregnancy can prevent Rh disease. Another shot may be administered after delivery and according to the American Pregnancy Association, “Rh-negative women should also receive treatment after any miscarriage, ectopic pregnancy, or induced abortion to prevent any chance of the woman developing antibodies that would attack a future Rh-positive baby.”

Positive Steps To Take If You’re Concerned

First off, try not worry! Remember that blood type is not a likely factor in most fertility problems. Other concerns like PCOS, tubal blockage or endometriosis, which can be addressed naturally, medically or through combination approaches, are far more common.

Many women who have type O blood go on to conceive, have healthy pregnancies and successful IVF treatments. Additionally, couples with “incompatible” (A-B-O) blood types often have no issues conceiving or carrying a pregnancy to term.

However, if you’ve had struggles and are concerned, you can benefit from a natural fertility program. A natural egg health program is a good choice if you’re concerned about egg quality. It’s important that both partners quit smoking, avoid secondhand smoke, and discontinue poor dietary choices as these are more significant factors than blood type in declining egg and sperm health.

If you’re worried you have an immunological fertility problem related to blood type, keep your immune system balanced with a Natural Fertility Diet and consider immune-boosting herbs for support. Do your best to stay at a healthy weight, and choose regular, low impact exercise as part of any fertility program.

Regardless of your blood type, a healthy diet and lifestyle is critical for fertility, conception, and pregnancy. We may never be able to control every possible factor related to our fertility. However, we can take charge of the foods we eat and how we live, and that can make all the difference.

  • Hagan, P. (2010, Oct.). Blood Group O Does Affect Your Chances of Having a Baby. Daily Mall. Retrieved from:
  • Hassanzadeh-Nazarabadi,M., Shekouhi, S., and Seif., N. (2012). The Incidence of Spontaneous Abortion in Mothers with Blood Group O Compared with other Blood Types. International Journal of Molecular and Cellular Medicine 1(2): 99-104. Retrieved from:
  • Scid V. J., Elies F.E. (2000). Immunohematological study of ABO hemolytic disease. Anales Espanoles de Pediatria 53:249–52. Retrieved from:
  • Rh Factor. (updated: March 2, 2017). American Pregnancy Association. Retrieved from
  • Schwartz, R. (2017). All About Rh Disease. Parents. Retrieved from:

Sarah has worked in the field of natural foods and herbalism for over 20 years. She’s the Co-Author of “Healthy Healing” with over 1 million copies sold, a Certified Herbalist, and a health and wellness consultant. Sarah Graduated from the Professional Herbal Studies program at East West School of Herbology, and holds a Bachelor’s Degree in English from St. Mary’s College. Working with women on their journey to wellness is her passion and she loves to share what she has been blessed to learn from naturopaths and other herbalists over the years.

Dr. Traxler is a University-trained obstetrician/gynecologist, working with patients in Minnesota for over 20 years. She is a professional medical writer having authored multiple books on pregnancy and childbirth textbooks and coursework for medical students and other healthcare providers and has written over 1000 articles on medical, health, and wellness topics. Dr. Traxler attended the University of Minnesota College of Biological Sciences and University of Minnesota Medical School, earning a degree in biochemistry with summa cum laude honors in 1981, and receiving her Medical Doctorate degree (MD) in 1986.

Preeclampsia or eclampsia

Preeclampsia, formerly called toxemia, is characterized by pregnancy-induced high blood pressure. It is accompanied by protein in the urine. Sometimes swelling due to fluid retention is also present. Eclampsia is the more severe form of this problem. This can lead to seizures, coma, or even death.

The cause of preeclampsia is unknown, but it is more common in first pregnancies. It affects about 5% to 8% of all pregnant women. Other risk factors for preeclampsia include:

A woman carrying multiple fetuses

A woman with high blood pressure, diabetes, and/or kidney disease before she became pregnant

A woman who is obese with a BMI greater than 30

Symptoms may include severe swelling of the hands and face, high blood pressure, headache, dizziness, irritability, decreased urine output, belly pain, and blurred vision. Treatment will vary according to the severity of the condition and the stage of the pregnancy. Treatment may include hospitalization, bed rest, medicine to lower blood pressure, and close monitoring of both the fetus and the mother.

Related Specialties

Online Medical Reviewer: Burd, Irina, MD, PhDGoode, Paula, RN, BSN, MSN

Date Last Reviewed: 12/1/2017

© 2000-2019 The StayWell Company, LLC. 800 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.

Screening and Prevention - Rh Incompatibility

Rh incompatibility can be prevented with Rh immune globulin, as long as the medicine is given at the correct times. Once you have formed Rh antibodies, the medicine will no longer help.

Thus, a woman who has Rh-negative blood must be treated with Rh immune globulin during and after each pregnancy or after any other event that allows her blood to mix with Rh-positive blood.

Early prenatal care also can help prevent some of the problems linked to Rh incompatibility. For example, your doctor can find out early whether you're at risk for the condition.

If you're at risk, your doctor can closely monitor your pregnancy. He or she will watch for signs of hemolytic anemia in your baby and provided treatment as needed.

Preventing Sensitization to Rh Factor

Sensitization to Rh factor can be thought of as developing a reaction to your baby's blood. If you are Rh-negative and you are exposed to Rh-positive blood, you can produce antibodies to Rh(D).

Blood cells from an Rh-positive fetus can enter your bloodstream during pregnancy and trigger the development of these antibodies. This can happen late in pregnancy or during delivery and also may happen if you have a miscarriage, abortion, or ectopic pregnancy.

If this is your first Rh-positive pregnancy, that fetus is usually not affected as it takes time for the antibodies to develop. In your future pregnancies, these antibodies can pass through the placenta and attack Rh-positive red blood cells ​in the developing fetus. This can lead to hemolytic disease   of the newborn or to pregnancy loss.

In order to prevent the formation of these antibodies, you may get an injection of RhoGAM (Rh immunoglobulin or RhIg). This injection contains antibodies that will attach to any Rh-positive cells. This prevents you from developing your own antibodies that can cause problems in future pregnancies or transfusions.

If you are Rh-negative, you will be given this injection at the 28th week of pregnancy   and again just after delivery if your baby is Rh-positive. If you have a miscarriage, trauma, or induced abortion, you will be given this shot within three days of the exposure. You will also be given this shot after invasive procedures such as amniocentesis, chorionic villus sampling, or fetal surgery.

While the RhoGAM injection is very effective, there is always the possibility that you will become sensitized to Rh factor despite treatment.

Blood Type Incompatibility or Jaundice

A-B-0 and Rh incompatibility happens when a mother’s blood type conflicts with that of her newborn child. Blood type incompatibility can be prevented, learn how.

What is blood type incompatibility? Jaundice?

Blood types are categorized by A, B, and O, and given an Rh factor of positive or negative. A-B-0 and Rh incompatibility happens when a mother’s blood type conflicts with that of her newborn child. It is possible for a mother’s red blood cells to cross into the placenta or fetus during pregnancy. When this occurs, the mother’s blood cells develop antibodies that can attack the newborn’s blood cells and cause jaundice. The risk of this is highest near or during delivery.

A-B-O incompatibility occurs when:

  • the mother is type O and the baby is B, A, or AB
  • the mother is type A and their baby is B or AB
  • the mother is type B and their baby is A or AB

Rh incompatibility occurs when a mother has Rh-negative blood and the baby has Rh-positive blood. The mother’s body will produce an auto-immune response that attacks the fetus or newborn’s blood cells as if they were a bacterial or viral invader. This immune response is fairly slow to develop and is rarely a serious issue in first pregnancies. However, subsequent pregnancies with an Rh incompatibility are a significantly higher risk.

Blood type incompatibility can be prevented with a blood test early in pregnancy. If an Rh incompatibility is found, an Rh-immune globulin treatment is administered about 28 weeks into the pregnancy. If the incompatibility is not detected, the newborn can develop severe jaundice leading to brain damage. While it can have serious consequences, jaundice in newborns is common and treatable medical attention is necessary at the first sign of yellowish discoloration in the skin or eyes.

Rh and ABO incompatibility in the infant results in jaundice, which is treated through hydration and phototherapy. Biliblankets and other phototherapy equipment help the infant’s body expel bilirubin, the cause of jaundice.

  • If the mother to be has bleeding or abdominal pain during pregnancy
  • Pregnancy which is ectopic or even an abortion that has been induced
  • An incompatible blood transfusion
  • Using an injection whose needle had blood which was Rh-positive test and also chorionic villus sampling (CVS) test can expose the pregnant woman to Rh positive blood

If the mother fails to get a RhoGam shot, she will be at risk of Rh incompatibility in her existing and all subsequent pregnancies