The first issue that must be addressed is whether the procedure itself will invalidate the clean days.
One halachic issue is the size of instruments used, since instruments of a certain size inserted in the uterus are presumed to bring on niddah status by uterine dilation. In the case of a standard hysteroscopy for polyp removal, the width of the instruments used is well under the 19mm measure used as a criterion by our site's halachic supervisor, Rav Yehuda Henkin. You should check with your doctor in advance to confirm the size of the instruments s/he will use, but it is likely that the instruments used will not invalidate the clean days.
The second issue is that of bleeding from the procedure. Given that the procedure involves direct removal of a polyp, you can expect to have bleeding for a number of days, followed by some spotting. There is disagreement among authorities as to the halachic status of this bleeding. Some maintain that when bleeding originates in the uterus, there is concern that hormonal changes may be involved and the woman is considdered niddah. The opinion of R' Henkin, however, is that this is a clear example of dam makkah, blood from a wound, which does not render a woman niddah. According to this view, bleeding from the procedure would not invalidate the clean days.
Nevertheless, you still need to have an acceptable bedikah on day 1 and day 7 to complete the clean days, and the bleeding from the procedure might make that difficult. Therefore, we recommend performing your hefsek taharah as usual, and daily bedikot up until you undergo the hysteroscopy. After the procedure you may disregard the bleeding and omit bedikot until the bleeding subsides. If you are able to perform a clean bedikah on day 7, you should do so and may immerse that night. If you are still bleeding by day 7, you may wait another day or two to try to perform the final bedikah. The rule is that no more than five days may pass without a bedikah in order to continue counting the clean days. This means that if you performed bedikot on days 1,2 and 3 of the clean days, you may omit bedikot for up to 5 days before performing a final bedikah on day 9. If you only performed bedikot on days 1 and 2, you may only delay your final bedikah to day 8.
In the event that the bleeding lasts more than five days, you would unfortunately have to restart the clean days from the beginning. In this case, your original hefsek taharah would remain valid, so you would not need to do a new hefsek taharah. The day you get your first acceptable bedikah would be considered day 1 of your new seven clean days.
It is important to note that sometimes a woman may experience a few days of bleeding and then continue spotting afterwards. The spotting might not invalidate a bedikah, so if you're no longer actually bleeding by day 7/8/9 but are still spotting, you should try to perform a bedikah anyway. If there is a questionable stain on the bedikah, you can bring it to a halachic authority for evaluation, explaining your situation.
Please feel free to get back to us with any further questions.