Blood Type Inheritance: Parent and Child Blood Type Chart
The essentials
Each parent passes on one ABO gene (A, B or O) and one Rh gene (positive or negative), so a child's blood type is a mix of both parents, not a copy of either. A and B show up whenever they are inherited, while O and Rh negative stay hidden unless the child gets them from both parents. Blood typing alone cannot prove who a parent is.
How do I read my baby's blood type result?
In the United States, a baby's blood type is often checked on cord blood at birth when the mother is Rh negative, and sometimes when she is group O positive[8]. Here, a fictitious report:
| Test | Result | Reference range | Flag |
|---|---|---|---|
| Mother: ABO group / Rh(D) type | O Pos | - | - |
| Mother: antibody screen | Negative | Negative | - |
| Cord blood: ABO group | A | - | - |
| Cord blood: Rh(D) type | Positive | - | - |
| Cord blood: direct antiglobulin test (DAT) | Negative | Negative | - |
- ABO group and Rh type: letters and a sign, not numbers; any of the eight types is normal[6].
- Antibody screen: looks for unusual antibodies in the mother's blood; every pregnant woman should have it with her blood type[8].
- Baby A positive, mother O positive: perfectly possible. A group O mother can only pass on O, so the A came from the father[2].
- DAT: negative, so no maternal antibodies coat the baby's red cells; our Coombs test guide explains it.
Your child's type does not match yours and you want to understand why? BloodSense explains each line of your report in plain words and helps you prepare your questions.
Explain my blood type reportHow are blood types inherited?
Blood type is inherited, like eye color[1]. Everyone carries two copies of the ABO gene, one from each parent, and passes one of them, at random, to each child[2]. The A and B versions make enzymes that add the A or B marker to red cells; the O version carries a small deletion that leaves it inactive[3]. That explains the rules:
- A and B are both expressed. A child with one A and one B is group AB.
- O is hidden behind A or B. A person with the gene pair AO is group A; BO is group B. Only OO gives group O[2].
- Rh works the same way, with two options. The gene for Rh positive (D) hides the one for Rh negative (d); a child is Rh negative only after receiving d from both parents[2].
The routine test shows the type, not the hidden gene: a group A parent may be AA or AO. In people of European ancestry, Rh negative is almost always due to a complete deletion of the RHD gene[4]. How the test itself is done is covered in how to read ABO and Rh results.
Parent and child blood type chart: which types are possible?
These combinations follow directly from the rules above[1][2]. The order of the parents does not matter.
| Parents | Possible child types | Not expected |
|---|---|---|
| O and O | O | A, B, AB |
| O and A | O, A | B, AB |
| O and B | O, B | A, AB |
| O and AB | A, B | O, AB |
| A and A | A, O | B, AB |
| A and B | A, B, AB, O | none |
| A and AB | A, B, AB | O |
| B and B | B, O | A, AB |
| B and AB | A, B, AB | O |
| AB and AB | A, B, AB | O |
| Parents | Possible child types |
|---|---|
| Positive and positive | Positive, or negative if both carry a hidden d |
| Positive and negative | Positive or negative |
| Negative and negative | Negative |
To combine both, read each table separately: two A positive parents can have an O negative child if both carry O and d. Testing difficulties can cause exceptions[1].
What are the odds for each blood type?
Each pregnancy is a new draw with the same odds[2]:
- Two group A parents who both carry O (AO and AO): 3 chances in 4 of group A, 1 in 4 of group O.
- An AO parent and an OO parent: 1 chance in 2 of each, A or O.
- An AO parent and a BO parent: 1 in 4 each for A, B, AB and O.
- Two Rh positive parents who both carry d: 1 chance in 4 of an Rh negative child.
How often each type occurs in the population is a different question, answered in how common each blood type is; for example, about 15% of people in the US are Rh negative[5].
My child's blood type does not match the chart: why?
An unexpected type is not proof of anything. The Red Cross states that ABO typing is not enough to prove or disprove paternity or maternity[1]. Possible explanations, from most to least frequent:
- Common A recording or recall error: a type remembered wrongly or never actually tested. Retesting both parents comes first.
- Possible A different biological parent, including donor eggs or sperm. Only DNA testing answers this question.
- Rare Cis-AB: one gene carries both A and B, so an AB parent can have an O child[9]. It is the most frequent ABO subgroup in Korea, found in about 1 donor in 2,800, and more common in East Asia than elsewhere[10].
- Rare Bombay and para-Bombay types: the person lacks the base H substance and tests as group O, yet can pass on A or B. In one reported family, a mother typed as O had an AB baby; she turned out to be para-Bombay carrying B[11].
- Rare A stem cell or bone marrow transplant: more than half of transplants from unrelated donors involve some ABO mismatch, and the new marrow gradually takes over red cell production[12].
Other inherited traits follow similar rules: see thalassemia trait and HLA typing
What can make a blood type result wrong?
No fasting or preparation is needed for blood typing[6]. Before comparing a family's results, check:
- Each type comes from a written laboratory result, not memory or a donor card read years ago.
- Both steps of ABO typing, forward and back typing, were done[6].
- No transfusion in the previous weeks, which can blur the result; tell the lab if there was one.
- Any transplant is mentioned, since it can change the type measured afterward[12].
- A surprising result is repeated on a new sample, and the lab is asked about subgroups such as cis-AB[9].
For the draw itself, see what to expect at a blood draw.
Why does inheritance matter in pregnancy?
When an Rh negative mother carries an Rh positive baby, her body can make antibodies that cross the placenta and destroy the baby's red cells[7]. This is why the father's type matters: if he is Rh positive or his type is unknown, the mother usually receives an Rh immune globulin injection during pregnancy, and again after birth if the baby is Rh positive[7]. An Rh positive father who carries two copies of RHD will always have Rh positive children[4]. The baby's own Rh type can also be read from fetal DNA in the mother's blood, which can avoid unnecessary injections[4].
A group O mother and an A or B baby can also be mismatched; this is one cause of newborn jaundice, followed with the baby's total bilirubin and indirect bilirubin[8].
When should I see a doctor?
When to see a doctor
- Emergency: call 911 for heavy bleeding or a strong blow to the abdomen during pregnancy, or a newborn who is very sleepy, floppy or hard to wake.
- Within 24 to 48 hours if you are Rh negative and pregnant and have bleeding, an abdominal injury or a miscarriage, so the injection can be discussed[7], or if your newborn's skin turns bright yellow, the yellow keeps spreading, or the soles of the feet are yellow[8].
- At your next appointment to confirm your own type before or early in pregnancy, or to talk through a family result that does not fit the chart.
Questions to ask your doctor
- Has my own blood type been confirmed by a laboratory, and is it in my records?
- I am Rh negative: does the father's type change my care, and is a fetal RHD test available?
- Was my baby's blood type checked at birth, and what did the DAT show?
- Our family results do not fit the usual chart: could a subgroup explain it, and should we be retested?
Frequently asked questions
Is blood type inherited from the mother or the father?
From both. Each parent gives one ABO gene and one Rh gene, so the child's type can match the mother, the father, both or neither[2].
Can a child have a different blood type from both parents?
Yes. Two A parents can have an O child, and an A parent and a B parent can have an AB or O child[2].
Do brothers and sisters always share a blood type?
No. Each child receives a new random combination from the same parents, so siblings can have different types[2].
Related tests
- Blood type testHow ABO and Rh are measured and who can donate to whom
- Rarest blood typeHow common each type is, from AB negative to Rh null
- Coombs testThe antibody test used in pregnancy and at birth
- Total bilirubinHow newborn jaundice is measured
- Sickle cell diseaseAnother blood trait passed from both parents
- American Red Cross. Blood Types Explained. redcrossblood.org (accessed November 12, 2026)
- Carter BloodCare. Genetic blood type explained. 2022. carterbloodcare.org (accessed November 12, 2026)
- Yamamoto F, Clausen H, White T, et al. Molecular genetic basis of the histo-blood group ABO system. Nature. 1990;345(6272):229-233. doi:10.1038/345229a0 (accessed November 12, 2026)
- Flegel WA. The genetics of the Rhesus blood group system. Blood Transfus. 2007;5(2):50-57. doi:10.2450/2007.0011-07 (accessed November 12, 2026)
- Stanford Blood Center. Blood types. stanfordbloodcenter.org (accessed November 12, 2026)
- MedlinePlus. Blood typing. U.S. National Library of Medicine. medlineplus.gov (accessed November 12, 2026)
- MedlinePlus. Rh incompatibility. U.S. National Library of Medicine. medlineplus.gov (accessed November 12, 2026)
- MedlinePlus. Newborn jaundice. U.S. National Library of Medicine. medlineplus.gov (accessed November 12, 2026)
- Yazer MH, Olsson ML, Palcic MM. The cis-AB blood group phenotype: fundamental lessons in glycobiology. Transfus Med Rev. 2006;20(3):207-217. doi:10.1016/j.tmrv.2006.03.002 (accessed November 12, 2026)
- Chun S, Choi S, Yu H, Cho D. Cis-AB, the blood group of many faces, is a conundrum to the novice eye. Ann Lab Med. 2019;39(2):115-120. doi:10.3343/alm.2019.39.2.115 (accessed November 12, 2026)
- Mohan G, Vaidya A, Shastry S. Neonatal testing leading to the identification of B(h) para-Bombay phenotype in the mother: case report with review of the literature. Immunohematology. 2021;37(2):59-63. doi:10.21307/immunohematology-2021-008 (accessed November 12, 2026)
- Staley EM, Schwartz J, Pham HP. An update on ABO incompatible hematopoietic progenitor cell transplantation. Transfus Apher Sci. 2016;54(3):337-344. doi:10.1016/j.transci.2016.05.010 (accessed November 12, 2026)
This page is general information. It does not replace the advice of a doctor or midwife, who interprets blood types with your history, your pregnancy and your laboratory's methods.
