To B+, or B-, is Blood Type the Question?
How Blood Type Can Affect Egg Donor Selection
Published in Fertility Today
By: Catherine Pateman,
Director of Case Management
Searching for an egg donor can be a challenging process. Most intended parents begin with a general search. They start looking for someone with basic genetic similarities to the intended mother such as eye color, hair color, height, and ethnic background. They may extend their search to look for someone with a similar educational background, religious background or even interests, such as the arts or athletics. Many intended parents are often mystified by the issue of blood type. Does the donor need to have the same blood  type as the intended mother? What happens if they are different? How does the intended father’s blood type affect things?
When considering blood type matching with an egg donor and whether it is important to you, there are a few factors to consider. One must first understand how an offspring’s blood type is determined. One must also consider the rarity, or frequency, of certain blood types. Another important reason to consider blood type matching is the issue of honesty with your child(ren) regarding their conception.
Intended parents Rob and Jennifer began their search for an egg donor with the intention to find someone to replace Jennifer’s genetics. They started with a basic search for a green-eyed, brown-haired donor with a height of at least 5’8’’. It seemed like simple enough criteria, but with the rarity of green eyes and such height amongst women, it proved to be a more difficult search than expected. When they finally came across donor Kelly, who was a great match for them on so many levels, they were ecstatic. As they read through her profile and learned more about her, they liked her even more.
When they got to the section regarding Kelly’s blood type, they paused. Rob and Jennifer both had a blood type of O+, as does 38% of the population (see Table A); they didn’t know what to make of Kelly’s AB- blood type. Kelly’s blood type represented a mere 1% of the population. Was it possible that their child could still have O+ blood type with this genetic parental combination? Would they be bringing a child into the world with a blood type as rare as Kelly’s?
Blood type in an offspring is determined by the parents’ blood type. There are three alleles (or versions) of the blood type gene: A, B, and O. Given the fact that everyone has two copies of these genes, one from each parent, there are six possible combinations; AA, BB, OO, AB, AO, and BO. These correlate to the four types of blood in the ABO system: A, B, AB, and O (AA and AO both translate to blood type A, just as BB and BO translate to blood type B).
Another factor in blood typing is called the Rh factor (or Rhesus factor), illustrated with either + or -. Since everybody has two copies of these genes, one from each parent, there are 3 possible combinations; ++, +-, or --. The + is dominant, so those with +- alleles are viewed as having Rh+ factor. Rh+ blood type is more common than Rh-. Almost 85% of Caucasians are Rh+, while the percentage is even higher for Asians, African-Americans, and Native Americans.1 The only way to guarantee a child will be born with a – blood type is if both parents are blood type –. If one parent is +, it is difficult to know if they are ++ or +-, therefore children born of two + parents can be born with either positive Rh factor or a negative Rh factor. Table C illustrates the possible Rh factor outcomes from various parental combinations.
Since Rob has blood type O, both of his alleles are O’s. Since donor Kelly has blood type AB, she has one A allele and one B allele. Their potential offspring’s possible blood types are illustrated in Table B; their child would have a 50% chance of having blood type A and a 50% chance of having blood type B.
Because Rob and Jennifer were both of O+ blood type, they could only create a child with blood types O+ or O-. Tables B and C show the various combinations that intended father Rob and donor Kelly could end up creating in a child ; A+, A-, B+ or B- blood types, each with population percentages varying from 2% to 34%.
Rob and Jennifer had not considered how genetically impossible differences in ABO type between parents and child might be revealed later in life. They realized this fact would influence their decision to be honest with their child. Rob and Jennifer had always assumed they would end up telling their child(ren) about their unique creation with the assistance of an egg donor. Because of the different potential blood types the child(ren) may have with donor Kelly’s genes, and that there was no layover in blood types Rob and Jennifer could create on the their own, deciding to move forward with donor Kelly would ultimately force them to be honest with their child(ren). Was that a decision they were ready to commit to?
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