I read that, of all the cases of couples struggling to conceive, one-third are about the woman’s infertility, one-third the man’s infertility, and one-third both or undetermined.
Before fertility clinics existed, some couples who married young did not conceive until they were much older. Sometimes life happens when least expected.
I had one acquaintance who was married for a dozen years with no children, but conceived immediately when they moved to the Southern Hemisphere.
It’s almost as if we just don’t understand human biology very well.