I read this years ago in a collection of Larry Niven short stories and fell in love instantly.
http://www.rawbw.com/~svw/superman.htmlMan of Steel, Woman of Kleenex
It discusses the medical pitfalls involving sex and insemination at the hands of Superman.
I've met Larry Niven and the man is just too much fun. He also invented the word -- which escapes me at the moment -- which means 'sex outside of your species but within the homonids' -- Spock's parents engaged in this practice. Scientifically it's also kind of come to mean sex between varients of a species, like diferent kinds of penguins mating. And probably things like lion/tiger crossbreeeds.