Fertility preservation, in simple terms, means storing human eggs, sperms, or embryos (fertilised eggs) for use in the future to achieve a pregnancy. The basis for preserving fertility is the observation that the chances of conception significantly decline from the mid-thirties onwards.
By mid-forties, women will have a hard time conceiving. The same trend is also observed as men age. But there are medical reasons as well for considering fertility preservation. Once preserved (usually in a frozen state) eggs, sperms or embryos remain viable for use at a convenient time in the future.