How to use
- Choose the father's ABO type and Rh factor.
- Choose the mother's ABO type and Rh factor.
- Read the possible and impossible blood types for the child.
Options explained
- ABO type
- Set by the A, B and O alleles; A and B are dominant over O. A type A parent may carry O, so two type A parents can have a type O child.
- Rh factor
- Rh positive is dominant. Two Rh-negative parents always have an Rh-negative child; otherwise both are possible.
ABO inheritance chart
| Parents | Possible child types |
|---|---|
| A × A | A, O |
| A × B | A, B, AB, O |
| A × AB | A, B, AB |
| A × O | A, O |
| B × B | B, O |
| B × AB | A, B, AB |
| B × O | B, O |
| AB × AB | A, B, AB |
| AB × O | A, B |
| O × O | O |
Frequently asked questions
Does an unexpected blood type prove someone is not the parent?
No. Rare types such as Bombay and cis-AB, and testing errors, can break the usual rules. Only a DNA test can establish parentage.
What can an AB parent and an O parent have?
A or B only — not AB or O, except in the rare cis-AB case.
What if the mother is Rh negative?
If the baby is Rh positive there can be Rh incompatibility. Tell your midwife or doctor, who will advise on tests and treatment.
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