Calculate your baby's possible blood types and genetic probabilities based on the parents' ABO and Rh factors.

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Curious about what blood type your baby might have? This tool uses classic Mendelian genetics to calculate all possible blood types and their probabilities for your child based on the parents' ABO blood types (A, B, AB, O) and Rh factors (+/-). Blood type refers to the type of antigens on the surface of red blood cells, which is determined by alleles inherited from both parents. Our calculator uses the rules of codominance and recessive inheritance in the ABO blood group system, along with the dominant-recessive relationship of the Rh factor, to estimate these probabilities. The results are displayed in a clear list to help you understand the genetic possibilities.
Q: If both parents have type O blood, what blood type could their child have?
A: The child can only have type O blood. Because the allele for type O blood is a recessive homozygote (ii), both parents can only pass on the 'i' gene. Therefore, the child's genotype must be 'ii', resulting in type O blood.
Q: Is there a risk for an Rh-negative (Rh-) mother having a second child? Can this calculator assess that?
A: This tool is only intended for estimating blood type probabilities and cannot assess the risk of hemolytic disease of the newborn (HDN). If the mother is Rh-negative and the father is Rh-positive, the fetus may be Rh-positive. During the delivery of the first child, the mother may be exposed to the fetus's Rh-positive red blood cells and produce antibodies, posing a hemolytic risk to subsequent Rh-positive pregnancies. For medical risk assessments like this, please consult a healthcare professional and undergo prenatal testing.
The results provided by this tool are probabilistic predictions based on standard genetic rules, not absolute diagnostic certainties. The actual blood type of your child must be confirmed by medical testing after birth. The calculation process does not involve uploading any personal data; all computations are performed locally in your browser, ensuring your privacy and security. This tool is not suitable for evaluating rare blood group systems (such as MNS, Kell, etc.) or genetic mutations.
The ABO blood type is controlled by a single genetic locus on chromosome 9, which has three alleles: A, B, and O. A and B are codominant, while O is recessive. Therefore, genotypes AA or AO result in type A blood, BB or BO result in type B blood, AB results in type AB blood, and OO results in type O blood. The Rh blood group system is more complex and involves multiple genes, but it is typically simplified by the presence or absence of the D antigen into Rh-positive (has D antigen) and Rh-negative (lacks D antigen), with Rh-positive (Rh+) being dominant over Rh-negative (Rh-). A typical example: The father is type A Rh+ (genotype could be AA or AO, Dd or DD), and the mother is type B Rh- (genotype could be BB or BO, dd). Their child could be type A, B, AB, or O in the ABO system. In the Rh system, as long as the father passes on a D gene, the child will be Rh+. Therefore, the child's blood type could be A Rh+, B Rh+, AB Rh+, or O Rh+, but Rh- is impossible unless the father's genotype does not carry the D gene (extremely low probability). When using this tool, if you have questions about the genetic mechanisms, you can refer to the principles explained below the results.