From: Rabbi Moshe Sofer
To: Rabbi Avraham
A woman who saw blood three times during marital relations was examined by a non-Jewish physician who claimed the blood originated from the sides of the vaginal canal, not the uterus. The Chasam Sofer rules that a non-Jewish physician cannot be relied upon here because physicians are suspected of boasting to enhance their reputation, and even a Jewish physician should not be relied upon alone when examination is possible; however, if the woman experiences pain in her sides during relations, this circumstantial evidence combined with physician testimony permits leniency, and he recommends a physical examination using a thick cloth wrapped around a probe as a practical solution.
Source: Shu"t Chasam Sofer YD §175