What parental blood types can produce one child with A positive (A+) and one with O positive (O+) blood type?

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Parental Blood Types That Can Produce A+ and O+ Children

For parents to have one child with A+ blood type and another with O+ blood type, the most likely combination is a mother with blood type O and a father with blood type A, both being Rh positive.

Blood Type Inheritance Patterns

The inheritance of blood types follows specific genetic patterns:

ABO Blood Group Inheritance

  • The ABO blood group is determined by three alleles: A, B, and O
  • A and B alleles are codominant (both expressed when present together)
  • O allele is recessive to both A and B

Rh Factor Inheritance

  • Rh positive (Rh+) is dominant over Rh negative (Rh-)
  • A person with Rh+ can be either homozygous (RhRh) or heterozygous (Rhrh)
  • A person with Rh- must be homozygous (rhrh)

Possible Parental Combinations

To produce children with both A+ and O+ blood types, the following parental combinations are possible:

  1. Mother O+, Father A+ (most common scenario)

    • Mother's genotype: OO Rh+
    • Father's genotype: AO Rh+
    • Possible children's blood types: A+ (AO Rh+) or O+ (OO Rh+)

  2. Mother A+, Father O+

    • Mother's genotype: AO Rh+
    • Father's genotype: OO Rh+
    • Possible children's blood types: A+ (AO Rh+) or O+ (OO Rh+)

  3. Mother A+, Father A+

    • Mother's genotype: AO Rh+
    • Father's genotype: AO Rh+
    • Possible children's blood types: A+ (AA or AO Rh+) or O+ (OO Rh+)

Clinical Implications

ABO Incompatibility Risk

  • When a mother has blood type O and children have blood type A, there is risk for ABO incompatibility
  • This occurs because mothers with type O naturally have anti-A antibodies that can cross the placenta
  • Research has shown that the risk of hyperbilirubinemia due to ABO incompatibility is greater for the second child than for the first if the mother is type O and the children are type A 1
  • The severity of ABO hemolytic disease varies based on the strength of the A antigen in the newborn 2

Rh Incompatibility Risk

  • Rh incompatibility occurs when an Rh-negative mother carries an Rh-positive fetus
  • This is not a concern in the scenarios above since both parents are Rh-positive
  • If one parent were Rh-negative, additional considerations would be necessary

Testing Recommendations

If ABO incompatibility is suspected:

  • Monitor newborns for jaundice more frequently (every 8-12 hours) 3
  • Consider testing cord blood for the infant's blood type and direct antibody test if maternal blood is group O 3
  • Be aware that the strength of the A antigen varies among newborns, affecting susceptibility to hemolytic disease 2

Important Considerations

  • The variation in A antigen strength among newborns is an unpredictable factor in the etiology of ABO hemolytic disease 2
  • Infants with relatively weak A antigen may tolerate maternal anti-A antibodies better than those with stronger A antigen expression 2
  • When the mother has blood type O, there is a 5.5 times higher likelihood of erythrocyte sensitization compared to mothers with blood types A or B 4

Understanding these blood type inheritance patterns is important for genetic counseling and anticipating potential hemolytic disease of the newborn in subsequent pregnancies.

References

3
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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