As women grow older, regular mammograms should be done to keep the Big C at bay. But do you know when you should have it? Experts suggest to keep your menstrual cycle in mind before you schedule your breast cancer screening. Based on studies, mammograms were most accurate in the first week of the cycle for women ages 35 to 54 who had been screened in the past two years. That's because the breast density is lowest at this time so it's easier to find malignancies. Try to schedule your test the first week for more accurate results.