Introduction

Pregnancy is a fascinating journey, but it can present complexities, particularly when it comes to differences in blood groups between the mother, father, and fetus. Having some basic understanding of blood group compatibility and its implications on pregnancy can help with planning efforts and reduce uncertainty among our audience. Conclusively, we explore different blood groups in pregnancy, required tests, available treatments, and potential risks associated with blood group incompatibilities.

Different Blood Groups

Blood groups are classified based on the presence of specific proteins on the surface of red blood cells (RBCs, the carriers of oxygen in the blood), known as antigens. While a variety of categories exist, the most well-known systems are the ABO blood group and the Rhesus (Rh) factor.

Each parent provides each child with a single gene for the ABO and Rh groups, with the combination of the two parental genes determining the final blood group of the child in each category.

The ABO system classifies blood into four types based on the presence or absence of A and B antigens. This means that the A and B are dominant over O, creating the following blood groups:

• A (either AO or AA genotype)
• B (either BO or BB genotype)
• AB (presence of both antigens)
• O (absence of both antigens)

The Rh system, primarily focused on the D antigen, categorizes individuals into either Rh-positive (D present) or Rh-negative (D absent) groups. Given that we inherit one gene from each parent, the presence of D antigen in one or both of those genes results in a Rh-positive blood group. Approximately 15% of individuals are classified as Rh-negative, while the rest are Rh-positive. 

Blood Group Incompatibility

Incompatibility occurs when two blood types with different antigens meet in a person’s body. This does not always turn into a serious reaction. However, it is one of the causes of a serious side effect of blood transfusion or organ transplant. The serious reaction occurs when a host with a negative status (either Rh negative or the absence of A, B, or both antigens) receives blood containing that same antigen that the host is missing. For example, if a person with the A blood group receives blood containing the B antigen, this reaction occurs. The host, missing an antigen, perceives that antigen as an offending agent and attacks it with antibodies, leading to the destruction of any cells containing that surface antigen. This process, called hemolysis, could be potentially fatal if not treated promptly.

The Role of Blood Groups in Pregnancy

The Rh factor plays a more critical role in pregnancy than the ABO category, while they both can impact the outcome. This emphasizes the importance of early screening and intervention to mitigate these risks.

In an Rh-positive mother, there is no risk of Rh incompatibility between the mother and fetus, and no risk of hemolysis or immune reaction to threat the pregnancy, since the mother has the D antigen on her own blood cells and thus, it is not considered foreign to the mother’s immune system.

However, in a Rh-negative mother, the father’s blood group is a key factor in determining the potential for Rh incompatibility. Since the fetus inherits genetic material from both parents, the father’s Rh status can influence whether the fetus is Rh-positive or Rh-negative. As a result, if the father is also Rh-negative, the fetus will be Rh-negative, eliminating the risk of Rh incompatibility. However, if the father is Rh-positive, there is a chance the fetus will also be Rh-positive, which may lead to complications in a Rh-negative mother.

It is worth noting that, in the first exposure of a Rh-negative mother to a Rh-positive baby, the reaction and hemolysis are not usually severe, and less aggressive treatments are required. This is why it is also important to determine whether this is the first time a Rh-negative mother is exposed to a Rh-positive baby, for an appropriate treatment plan.

Tests for Blood Group Compatibility

When paternity is certain (the blood group and Rh status of the father are known), testing can help determine whether interventions such as the Rh immunoglobulin (RhIG), commonly known as RhoGAM, are necessary. If the father is Rh-negative, RhIG administration may be avoided, reducing unnecessary testing or exposure to blood products. However, in cases where paternity is uncertain or the father’s Rh status is unknown, RhIG is typically recommended as a preventive measure, due to the higher risk of damage in case of Rh incompatibility.

Routine prenatal care includes blood tests to assess the mother’s blood type, Rh status, and antibody levels. These tests are critical for identifying potential incompatibilities early in pregnancy. The following tests are recommended as part of routine pregnancy care:

• Maternal blood typing and antibody screening: To determine the mother’s blood type (ABO and Rh) and screen for antibodies. Higher levels of antibodies could indicate prior exposure and sensitization to Rh-positive blood.
• Paternal Rh testing: In a Rh-negative mother, testing the father’s Rh status can provide clarity on the potential for Rh incompatibility and the need for RhIG. 
• Fetal Blood Group Genotyping (FBGG): Advancements in prenatal screening, such as noninvasive fetal blood group and Rh genotyping, allow clinicians to determine the fetus’s Rh status using maternal blood samples. This test analyzes fetal DNA circulating in the mother’s bloodstream and helps avoid unnecessary RhIG administration if the fetus is Rh-negative.
• Quantifying feto-maternal hemorrhage: In cases of significant hemorrhage (e.g., trauma), tests like the Kleihauer-Betke test or flow cytometry may be used to quantify fetal blood in the maternal circulation, determining if additional RhIG doses are needed.
• Post-Delivery testing: After birth, especially in the first pregnancies of Rh negative mothers, the baby’s blood type is tested to confirm Rh status. If the baby is Rh-positive, the mother receives a postpartum RhIG injection to prevent sensitization for future pregnancies.

These tests enable healthcare providers to tailor care, ensuring timely interventions to protect both the mother and fetus.