Blood Group

The blood group test provides essential information for transfusion safety by determining whether an individual belongs to group A, B, AB or 0 and identifying their Rh status. This test prevents the risk of blood incompatibility and helps in rapidly selecting the correct blood product in emergencies. This approach directly supports clinical safety.

Blood group classification is based on the identification of antigens on the surface of erythrocytes. The combined evaluation of the ABO and Rh systems prevents possible hemolytic reactions. In this way, surgical procedures, childbirth processes and emergency care interventions can be planned safely.

Blood group compatibility analysis is especially important in determining the risk of Rh incompatibility during pregnancy. Early detection allows the use of immunoprophylaxis and prevents hemolytic disease of the newborn. Thus, a high level of protection is achieved for both maternal and neonatal health.

Blood group determination plays a critical role in organ transplantation, the use of plasma products and public health screening programs. Regular recording and follow-up systems support national blood banking processes, increase accessibility and strengthen the reliability of emergency blood supply.

What Is a Blood Group?

A blood group is a genetic characteristic classified according to the antigen structures on the surface of a person’s red blood cells. The most common systems are the ABO and Rh (positive/negative) systems. For example, there are four main groups — A, B, AB and 0 — and each of these can be Rh positive or negative. Knowing the blood group is vital for compatibility in blood transfusion, organ donation and pregnancy.

So what is the Rh factor that determines whether we are “positive” or “negative”?

When you state your blood group (for example, “A Positive” or “0 Negative”), the second part refers to the Rh (Rhesus) system. This is a second identity system that is completely separate from ABO.

The Rh system is very complex and contains dozens of different antigens, but the one that is clinically most important for us is a single antigen called the “D” antigen. Just like A and B, you can think of it as a “D flag”.

If a person’s red blood cells have this D antigen (D flag) on their surface, that person is considered Rh positive (Rh+).

If a person does not have this D antigen, they are considered Rh negative (Rh–).

Unlike the ABO system, an Rh-negative person does not naturally produce Anti-D antibodies (the “soldiers” that attack the D flag) unless they are exposed to Rh-positive blood. For the immune system to produce these antibodies, it must first “meet the enemy”, that is, Rh-positive blood. This encounter may occur through an incorrect blood transfusion or, most commonly, when an Rh-negative mother carries an Rh-positive baby. This is called “sensitization” and forms the basis of what we refer to as “blood incompatibility” in pregnancy.

What is “blood incompatibility” (Rh incompatibility) in pregnancy?

When we talk about “blood incompatibility”, this is the most serious and important situation we mean medically. It occurs only under a specific scenario.

• Mother: Rh Negative (Rh–)
• Father: Rh Positive (Rh+)

In this situation, the baby to be born has a chance of being Rh positive (Rh+) (depending on the father’s genetics, this may be 50% or 100%). If an Rh-negative mother is carrying an Rh-positive baby, there is an “incompatibility”. The baby’s blood has a different “flag” (the D antigen) from the mother’s blood.

The problem usually does not appear in the first pregnancy. During pregnancy, the mother’s and baby’s circulations are mostly separated. However, at the time of birth, during miscarriage, ectopic pregnancy or a bleeding episode in pregnancy, a small amount of Rh-positive fetal blood cells may cross the placenta and mix into the Rh-negative maternal circulation.

The mother’s immune system recognizes these Rh-positive cells (cells with the D flag) as a “foreign invader”. In response, it begins to produce ‘Anti-D’ antibodies (defense soldiers) to destroy this D flag. Once the mother starts to produce these antibodies, she becomes “sensitized”, and these antibodies remain in her body for life. The first baby is usually not affected by this slowly developing immune response.

How can blood incompatibility harm the baby?

The real danger begins in the second or subsequent pregnancies. If the mother becomes pregnant again with an Rh-positive baby, the ‘Anti-D’ antibodies already present in her body act very rapidly and strongly this time. These antibodies (they are of the IgG type) easily cross the placenta, enter the baby’s circulation and start to attack and destroy the baby’s Rh-positive blood cells.

This attack leads to a serious condition known as “Hemolytic Disease of the Fetus and Newborn” (HDFN). This literally means the baby’s blood is being broken down within its own body. The consequences of this can range from mild to life-threatening.

The most common effects include:

• Anemia
• Neonatal jaundice
• Enlargement of the liver and spleen
• Heart failure
• Generalized body edema (Hydrops fetalis)
• Intrauterine death

Severe anemia causes the baby’s heart to go into failure and can result in fluid accumulation throughout the body (Hydrops fetalis), which is the most serious and life-threatening form.

Is it possible to prevent Rh blood incompatibility today?

Yes, it is absolutely possible. The prevention of Rh incompatibility is one of modern medicine’s greatest success stories. The solution is a protective injection called “Anti-D Immunoglobulin” (RhIg), commonly known as the “anti-D shot” or “incompatibility injection”.

This injection works somewhat like a vaccine but is actually a passive immunization. Its content is ready-made, concentrated ‘Anti-D’ antibodies.

The logic is as follows: When this injection is given to an Rh-negative mother, these ready-made antibodies quickly find any Rh-positive fetal blood cells that may have entered the mother’s circulation and attach to them, silently clearing them away before the mother’s own immune system has a chance to recognize them and react.

Thanks to this “clean-up operation”, the mother’s immune system never truly sees the “D flag”. As a result, her own Anti-D antibody factory (memory cells) is never established, and the mother remains “nonsensitized”. This means she will not pose a threat to future Rh-positive babies.

When should the incompatibility injection (RhIg) be given?

The timing of this injection is critical in preventing sensitization of the mother. There are standard times and situations in which an Rh-negative mother (if there is a risk of exposure to fetal blood) should receive the injection:

These situations include:

• 28th week of pregnancy (for routine prophylaxis)
• After delivering an Rh-positive baby (within the first 72 hours)
• Miscarriage (spontaneous abortion)
• Termination of pregnancy (abortion)
• Ectopic pregnancy diagnosis or treatment
• Vaginal bleeding during pregnancy
• Amniocentesis or Chorionic Villus Sampling (CVS)
• Significant trauma to the abdominal area

Does IVF treatment affect blood incompatibility risk?

A pregnancy achieved via IVF does not differ in terms of blood incompatibility risk from a pregnancy conceived naturally. The risks are the same, and the same precautions (the injection at 28 weeks and postpartum) are taken.

However, some specific steps within the IVF process itself create additional moments that carry a “sensitization” risk for an Rh-negative woman. Therefore, IVF clinics must pay special attention to this issue.

The most important step is Oocyte Pickup (OPU), or egg collection. This procedure is performed by passing a needle through the vagina to reach the ovaries. Although it is a minimally invasive procedure, some internal or vaginal bleeding can occur.

If an Rh-negative woman is undergoing treatment with an Rh-positive partner (or Rh-positive sperm donor) and an egg collection procedure is performed, there is a theoretical risk of sensitization during this procedure. For this reason, in modern IVF practice, administering a prophylactic anti-D immunoglobulin (RhIg) injection within 72 hours after egg collection is a standard and safe approach for such patients.

Similarly, miscarriages or ectopic pregnancies after IVF treatment are situations that require an RhIg injection, just as they do in natural pregnancies.

What about ABO blood group incompatibility? Is it dangerous too?

Yes, there is also ABO incompatibility. This condition is much more common than Rh incompatibility but is almost always much milder.

ABO incompatibility is usually seen in the following scenario.

• Mother: Blood group 0
• Baby: Blood group A or B

As you may recall, women with blood group 0 naturally have both Anti-A and Anti-B antibodies in their blood. Those antibodies of the IgG type can cross the placenta and attack the baby’s A or B blood cells.

However, this attack is not as severe as in Rh incompatibility. The A and B antigens on the baby’s blood cells do not trigger an immune response as strong as the Rh (D) antigen.

The most common manifestation of ABO incompatibility is neonatal jaundice starting in the first 24 hours of life. This condition is usually easily managed in the hospital with “phototherapy” (blue light treatment). The need for exchange transfusion or the development of severe fetal anemia (Hydrops fetalis) is almost never seen in ABO incompatibility.

Is the claim that people with blood group 0 have a lower ovarian reserve true?

This is one of the questions we most frequently hear from our patients and stems from common concerns arising from some studies that reached the media years ago.

About 10–15 years ago, a study conducted in the United States suggested that among women undergoing infertility treatment, those with blood group 0 were twice as likely to have high levels of FSH — a hormone indicating reduced ovarian reserve — compared with women with blood group A. This finding led to the hypothesis that blood group 0 could be a risk factor for “early ovarian aging” and caused considerable public concern.

However, science does not draw conclusions based on a single study. Following this, new studies were conducted in different parts of the world with much larger patient groups.

What does science now say about this “blood group and infertility” claim?

The results of subsequent studies started to contradict the initial findings. For example, a very large study from China involving tens of thousands of women found the exact opposite: it suggested that blood group 0 might be protective, and that having blood group B or AB was associated with diminished ovarian reserve.

When such completely opposing results appear, scientists usually conclude that these weak associations are likely not due to the blood group itself, but to other, unaccounted-for genetic factors (confounding variables) such as the ethnic backgrounds of the studied populations.

The final word on this subject came from a large systematic review and meta-analysis published in 2017. Meta-analyses are the highest level of scientific evidence, as they combine all reliable studies on a topic and analyze the data collectively.

This large analysis examined data from more than 55,000 women and reached a clear conclusion: there is no statistically significant relationship between women’s ABO blood group (A, B, AB or 0) and their ovarian reserve. This result did not change regardless of whether ovarian reserve was measured by FSH or by AMH, which is a more reliable and currently gold-standard marker.

Which tests should we rely on when assessing your ovarian reserve?

When evaluating a woman’s fertility potential and her response to treatment, an IVF specialist relies on scientifically proven, reliable and robust markers. Your blood group is not one of these markers.

We tell our patients not to get caught up in such contradictory information they read online that causes unnecessary anxiety, but instead to focus on the real clinical picture. The main and reliable tests we use to understand ovarian reserve are:

• AMH (Anti-Müllerian Hormone) blood test
• Antral follicle count (ultrasound)
• Baseline FSH hormone

In conclusion: Having blood group 0 does not mean your ovaries contain fewer eggs or that your fertility is low. It does not provide a basis for predicting your treatment plan or chance of success.

Does my blood group affect the success of IVF treatment (embryo quality, implantation)?

This is a different question from ovarian reserve: “Does being blood group 0 mean my embryos will be of poorer quality or my implantation chance will be lower?”

The scientific evidence on this is also very clear: No, it does not.

Many retrospective studies have repeatedly shown that there is no difference between women with blood groups A, B, AB and 0 in the key stages of IVF treatment. Your blood group has no effect on:

• The total dose of hormones used
• The length of the stimulation period
• The total number of eggs collected
• The proportion of mature eggs
• Fertilization rates
• Embryo quality
• Clinical pregnancy rates
• Live birth rates

In other words, your blood group does not determine your response to treatment or embryo quality. Treatment protocols are not planned according to your blood group.

Does the combination of partners’ blood groups matter in IVF?

This is another hypothesis, especially considered in relation to the ABO system. For many years, it has been suggested that ABO incompatibility between partners (for example, a woman with blood group 0 and a man with blood group A) could cause infertility by leading to sperm antibodies in cervical mucus. However, since IVF achieves fertilization of egg and sperm in the laboratory, this theoretical barrier is already bypassed.

What about the implantation stage, when the embryo attaches to the uterus? Most studies have shown that the blood group combination of the parents does not affect pregnancy or live birth rates.

There is, however, one exceptional finding. In 2022, a large study from China examining more than 30,000 IVF couples reported a very interesting and specific result:

When both the mother and father had blood group AB (AB/AB couples), live birth rates were statistically significantly higher compared with all other blood group combinations.

This effect was not related to embryo quality, suggesting that it may occur at the implantation stage. A theoretical explanation is that a mother with blood group AB has no natural Anti-A or Anti-B antibodies in her blood. This “immunologically calm” state may make it easier for the embryo to be accepted.

However, this is the finding of a single study in a specific ethnic population. In science, such results must be confirmed by other studies before being generalized. Therefore, while it is an interesting research note, it does not currently change clinical practice or the way we counsel couples about their chances of success.

Frequently Asked Questions