Gestation is roughly the same time for unicorns that is is for humans - 9 months. The female then leaves the males territory and secludes herself in the forest for the winter. T hey are also said to be attracted to virgins, which is one way that they were hunted. Virgins represent purity, and a unicorn is very pure. By using a virgin, hunters were able to seek out unicorns and take their horns, killing them.
Unicorns are also able to detect virgins.
If the horn of a unicorn pierces the heart of the woman, she is not a virgin. This method is sometimes said to be applied to trustworthy and sincere people in general, such as in the Xanth books by Piers Anthony.