Troubleshooting

If you are unable to pass a uterine sound (usually because of stenotic os), consider a one- to two-week trial of vaginal estrogen (1gm Estrace or Premarin cream nightly). This carries a theoretical risk, if an estrogen responsive cancer is present, but may "soften" the cervix enough to let the sampling device or sound pass. In pre-menopausal women, rescheduling the procedure during her period may produce similar effect (but runs a higher risk of producing inadequate or difficult to interpret sample).
If you are unable to pass the sound, despite placement of the tenaculum on the anterior cervix, consider moving the tenaculum to the posterior cervix as this may better "straighten" the os, permitting the sampling device or sound to pass.
If you are unable to pass 3mm sampling device, sometimes a 4mm sampling device will pass, as it is a bit stiffer.
If the EMB procedure is too painful your patient, consider a combination of the available anesthetic options or refer to gynecology (for the procedure to be performed in the operating room).