Many of my friends (those who have had sex) have told me that, if I want to prevent pregnancy, the first three to four days right after the menstrual period is over are safe for sexual intercourse. Are they correct?

Yes and no. If you could be 100 percent certain that you ovulated exactly two weeks after your period began, then those days would be "safe." But no woman's body works that perfectly. Therefore, if you have unprotected sex in the days right after your period ends, you are playing Russian roulette. The odds are that there aren't any bullets in the gun, but it could happen and you'd wind up pregnant.

Natural planning can work relatively effectively, but for that to happen the woman has to be much more aware of her body. If she makes every effort to discover when she ovulates, including taking her temperature every morning and being on the lookout for the slight discomfort that accompanies ovulation, the odds of an unintended pregnancy can be greatly reduced. But if you do it in a haphazard manner, those odds increase dramatically.