Doubtless this has occured to some-- what about the barren-ness or relative infertility of the Elven race? After all, living thousands of years, most Elves only have one or two offspring. So what's up with birth control?
Naturally these questions have not been deeply explored by JRRT.
Nevertheless, let me hazard one extrapolation for the board: Elven sex was a rare event, occuring no more frequently than pregnancy among the Second-born.
Perhaps one of the consequences made by Elves who became mortal would be to become sexually active as the Second-born...