The short answer
There is no ethically or psychologically correct rule for deciding which father provides sperm. Couples usually work from two sets of inputs at once: what the clinical results suggest, and what each partner actually feels about a genetic link. Neither set outranks the other, and a counselor experienced in third-party reproduction is a reasonable place to have the conversation.
The clinical inputs
Both fathers can complete testing before the decision, which is often easier than deciding first and testing afterward. Expect:
- semen analysis
- genetic carrier screening, ideally on a panel comparable to the egg donor's
- medical and family history review
- infectious-disease testing on the clinic's required schedule
- a discussion of age, general health and medications
Sometimes results point clearly in one direction. Often they do not, and the decision stays where it started, with the two of you.
Screening does not eliminate risk. If a father and the donor carry the same recessive condition, that is a counseling conversation about reproductive risk, not an automatic disqualification of either person.
The personal inputs
- How much does a genetic connection matter to each of you, said out loud?
- Do you want siblings, and would you want them to share an egg donor?
- Do you both want to create embryos now, or would one of you rather preserve sperm and decide later?
- How would each of you feel if embryo yields turn out very uneven?
- Whose family history or cultural expectations are in the room, and do you agree about their weight?
Better questions than which one is the real dad
That framing arrives from relatives and strangers, and it is worth retiring inside your own household first. More useful versions:
- What would make each of us feel fully recognized as a parent?
- Which rituals and responsibilities belong to each of us, independent of genetics?
- How will we answer the resemblance comments that will come?
- What will we tell our child, at what age, and in what words? See telling your child.
Professional guidance strongly encourages age-appropriate disclosure to donor-conceived people about the fact of donor conception, while leaving the decision and the wording with parents. Deciding how you will talk about it tends to make the sperm-source question easier, not harder.
Who goes first is often the better question
Many couples create embryos with one father for a first child and hold a plan for the other: frozen sperm, reserved eggs, a sibling lot. That keeps the decision reversible longer, though donor availability, storage and budget all limit how long.
Protect the non-genetic father deliberately
Genetics does not determine parental commitment, but it can affect parentage strategy, documentation and citizenship analysis, so records must be accurate. Parentage rules, filing timing and court practice vary by state and continue to change, so the non-genetic father's protection is a question for your own attorney. See legal parentage and laws and policies.
Research on gay-father families formed through surrogacy generally reports strong parent-child relationships regardless of which father is genetically related. Those studies use small volunteer samples in particular countries, and no family structure guarantees an outcome. In practice, this decision weighs far more during planning than it does at year five.