Incompatible sperm and egg

My friend says that she knows a couple that are unable to have children. They went for examinations and both are fertile … he could impregnate another woman, and she could become pregnant by another man … but they aren’t compatible with each other. I’m skeptical. Is this possible?

Not so much incompatible gametes, as incompatible sperm and cervical mucous. She is probably producing antibodies that are killing off his sperm before it has time to get anywhere worthwhile.

Don’t have time to expand further, sorry!

Incompatible immunology is a possibility, and the solution to that is IVF. It could be something a bit more fundamental - sometimes, every combination of genes from two people just don’t add up to a viable embryo, or add up to one that will not implant, or one that is rejected by the mothers immune system (addressed by IVF+surrogacy). In many of these cases, a combination of AID (artificial insemination by donor), IVF and/or surrogacy is the only answer.

We are strange and complex beings - just because things work the way we think they should 99.999…% of the time, does not mean that things won’t fail some proportion of the time, and for some couples, that failure rate is 100%. Calling it incompatibility just covers a huge range of possibilities for convenience, and avoids detailed explanations.