From: Rabbi Moshe Sofer
To: Rabbi Yitzchak Nosson
The Chasam Sofer rules leniently regarding a woman who repeatedly sees blood during marital relations. He holds that a bedikah finding blood only on the sides of the testing instrument indicates a vaginal rather than uterine source, permitting her to her husband, and that if the shfoferes finds no blood at all she is likewise pure, defending the Bach's position at length. In all cases she counts seven clean days after each occurrence but is not required to divorce.
Source: Shu"t Chasam Sofer YD §181