Cut back on pap exams, doctors tell 20-somethings First mammograms. Now -- in an apparent coincidence -- Pap smears. New guidelines by the American College of Obstetricians and Gynecologists say most women in their 20s can have a Pap smear every two years instead of annually to catch slow-growing cervical cancer. The change comes amid a separate debate over when regular mammograms to detect breast cancer should begin, in the 40s or the 50s.