Blood Type O Only for Baby
When both parents have blood type O (father O+ and mother O-), the baby can only be blood type O. The baby will inherit either O positive or O negative, depending on the Rh factor inheritance.
ABO Blood Type Inheritance
Both parents with blood type O can only pass O alleles to their offspring, making it genetically impossible for the baby to have any other ABO blood type (A, B, or AB). This follows basic Mendelian inheritance patterns where:
- Father's genotype: OO (homozygous for O)
- Mother's genotype: OO (homozygous for O)
- Baby's possible genotype: OO only
Rh Factor Possibilities
The Rh status of the baby depends on the father's Rh genotype:
- If father is Rh+ homozygous (DD): All babies will be O positive
- If father is Rh+ heterozygous (Dd): Babies have 50% chance of being O positive and 50% chance of being O negative
Since the mother is Rh negative (dd genotype), she can only contribute a negative Rh allele.
Critical Clinical Consideration: Rh Incompatibility Risk
This pregnancy carries risk for hemolytic disease of the fetus and newborn (HDFN) if the baby is Rh positive. The Rh-negative mother can develop anti-D antibodies against an Rh-positive fetus, particularly in subsequent pregnancies 1.
Management Recommendations:
- Routine Anti-D immunoglobulin prophylaxis should be administered at 28 weeks gestation and after delivery if the baby is confirmed Rh positive 1
- Kleihauer-Betke test after delivery to assess fetomaternal hemorrhage and determine additional Anti-D dosing needs 1
- Cord blood testing at delivery for baby's Rh status and direct antibody test (Coombs' test) 2
- Monitor for neonatal jaundice in the first days of life, as hemolysis can continue postnatally even with prophylaxis 1
Common Pitfall to Avoid:
Do not assume this is a "low-risk" pregnancy simply because both parents are type O. The Rh incompatibility between O- mother and potentially O+ baby requires the same vigilant monitoring and prophylaxis as any other Rh-negative pregnancy 1, 3.