Why can't the gynecologist perform a colposcopy if a woman is on her period?

Oh say can you see?: The beginning of the National Anthem is the appropriate answer to your question. The Colposcope is basically a microscope on wheels that must visualize microscopic cells within the narrow opening of the cervix as well as the outside of the cervix. Menstrual blood is RED, the cells should be WHITE, and the MD is BLUE, because he/she can't make a diagnosis not seeing "from sea to shining sea."

Can't see!: It's VERY important to get a colposcopy if your pap is abnormal. A colposcopy is a speculum exam where special stains and magnifying lenses are used to look for pre-cancers on your cervix. If there are abnormalities, your GYN will take a biopsy. If you're on your period, sometimes it'll be hard for your doctor to see any lesions to biopsy so come on a different day.