Niddah 1:4-5

Niddah 1:4

A “virgin” for our purposes means any woman who has never experienced menstrual bleeding, even if she was married (and therefore not a virgin in the usual sense). A pregnant woman means from the time her pregnancy is apparent to those who look at her. A nursing woman means until she weans her child; if she gave the child to a wet nurse, weaned him or if the child died, Rabbi Meir says she conveys impurity retroactively for 24 hours but the Sages say that her time is sufficient for her.

Niddah 1:5

An “old” woman means any woman for whom three menstrual cycles have passed close to her old age (without her seeing blood). Rabbi Eliezer says that if a woman experienced three menstrual cycles (without seeing blood), after which she again sees blood, her time is sufficient. Rabbi Yosi says that if a pregnant or nursing woman experienced three menstrual cycles (without seeing blood), after which she again sees blood, her time is sufficient.