In females, changes in the primary sex characteristics involve growth of the uterus, vagina, and other aspects of the reproductive system. Menarche, the beginning of menstruation, is a relatively late development which follows a long series of hormonal changes. Generally, a girl is not fully fertile until several years after menarche, as regular ovulation follows menarche by about <answer>two years</answer>. Unlike males, therefore, females usually appear physically mature before they are capable of becoming pregnant.
How many years does regular ovulation follow menarche?
two years