The short answer
In routine clinical practice, one embryo is created from one sperm source and one egg source. A child born from that embryo is genetically related to one father. There is no standard clinical procedure that merges two men's genetic material into a single embryo.
That is a planning fact, not a statement about who is a parent.
What two fathers can do instead
Each father creates his own embryos with the same egg donor. A clinic may divide a fresh donor retrieval, or use separate frozen-egg lots, so that each father has an embryo cohort. Children born from those cohorts share the same egg donor and are half-genetic siblings. Egg number, egg maturity and laboratory protocol decide whether a split is possible or wise, so no one should promise you an even division or an equal embryo yield. See both fathers' embryos.
Each father uses a different egg donor. This creates a genetic link between each father and a different child. It also doubles donor screening, donor agreements, embryo creation, cost and the number of donor relationships your family will explain later.
One father provides sperm now, the other later or not at all. Some couples create embryos with one father and freeze sperm from the other, keeping the decision open longer.
About mixing sperm
The IVF laboratory always records which sperm source created each embryo. Combining specimens does not produce useful uncertainty. It introduces medical, legal and identity questions that later fall on the child, and it complicates records that may matter for parentage or citizenship. Ask the clinic to report fertilization and blastocyst results separately by sperm source.
Experimental technology is not something you can plan around
Research into creating gametes from other cell types appears in the news regularly. It is not available as routine clinical care, and no program should present it as part of a treatment plan. Build your family plan on what your clinic can actually do this year.
What matters more than the genetic split
The father who is not genetically related needs the same deliberate legal protection as the one who is. Parentage rules, filing timing and court practice vary by state and continue to change, so this belongs with your own attorney rather than a website. Start with legal parentage and laws and policies.
Studies of gay-father families formed through surrogacy generally report warm parent-child relationships and good child adjustment. Those studies use small volunteer samples in particular countries, and no family structure guarantees any outcome. What they do suggest is that the question of which father is genetically related carries far less weight in daily family life than it does during planning.
Questions worth asking early
- Do we both want a genetic connection, or does one of us feel strongly and the other not?
- Do we want siblings, and should they share an egg donor?
- How would we feel if the embryo yield is uneven between us?
- What will we tell our child, and when?
- What legal steps protect the non-genetic father where our carrier is likely to deliver?
A counselor experienced in third-party reproduction can keep this conversation from turning into a quiet hierarchy between partners.