Blood Type Compatibility for Pregnancy: ABO & Rh Factors Explained
ABO blood type does not determine fertility or ability to conceive. Any combination can produce a child. However, Rh factor matters for hemolytic disease of the fetus/newborn (HDFN).
ABO Inheritance (Child's Possible Blood Types)
| Parent 1 | Parent 2 | 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 only |
Rh Factor (Critical for Pregnancy)
- Rh+ = has D antigen; Rh− = lacks it
- If mother Rh−, father Rh+ → fetus may be Rh+
- Fetal RBCs enter maternal circulation → mother makes anti-D IgG
- Anti-D crosses placenta in subsequent pregnancies → destroys fetal RBCs → HDFN (anemia, jaundice, hydrops)
Prevention (Standard of Care)
- Rh− mothers receive Rho(D) immune globulin (Rhogam) at 28 weeks, within 72 hrs post-delivery if baby Rh+, and after any sensitizing event (amnio, bleeding, trauma, miscarriage, abortion)
- Effectiveness: >99% prevention of alloimmunization
ABO Incompatibility
Mother type O, baby A/B → mild hemolysis (anti-A/B are IgM, don't cross placenta well; some IgG does). Usually causes mild jaundice/anemia—much less severe than Rh disease. No prophylaxis needed.
Bottom line: ABO doesn't limit conception. Rh− mothers need Rhogam. Know your type.
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