For young women with a world of choices, even that monthly curse, the menstrual period, is optional. Thanks to birth control pills and other hormonal contraceptives, a growing number of women are taking the path chosen by 22-year-old Stephanie Sardinha. She hasn't had a period since she was 17. "It's really one of the best things I've ever done,'' she says. A college student and retail worker in Lisbon Falls, Maine, Sardinha uses Nuvaring, a vaginal contraceptive ring. After the hormones run out in three weeks, she replaces the ring right away instead of following instructions to leave the ring...