Responsa for Niddah 131:2

Q. A lived normally with his wife L for some time. Later, however, L detected discharges of blood during copulation on three occasions. Should L "examine herself" (Niddah 66a, with a lead tube, in order to discover whether the blood flows from the interior of the womb or from the walls of the vagina) or must A divorce her immediately? In case of divorce, is L entitled to her ketubah?
A. Rashi and Ri hold opposite views on this subject. We are not at liberty to disregard Rashi's view and, therefore, can not permit A to live with L even if an "examination" will produce favorable results. However, we must make the following distinction: If the three acts of copulation during which blood
was detected were consecutive, A must divorce L forthwith; but, if they were not consecutive and between each act there were other acts during which no trace of blood was detected, A is permitted to live with L. If the copulations during which blood was detected, occurred on specific dates, or at regular intervals, A must refrain from copulation on such dates. Moreover, if A is not anxious to remarry, and is willing to allow L to live away from him in another district and to deal with her through an intermediary or only in the presence of a third party, he does not have to divorce her. In case of divorce, however, L is entitled to the Ikkar-ketubah and to her dowry, but she cannot collect the additional jointure, since some authorities are of the opinion that under the circumstances she is not entitled to the additional jointure.
This Resp. is addressed to "my relative Rabbi Baruch ha-Kohen."
SOURCES: Am II, 49; Rashba I, 839, 40; Pr. 625; Mord. Niddah, 735; Hag. Maim., Isurei Biah 8, 3. Cf. Sefer ha Terumah 106–7; Maharil, Responsa 173.

We have carefully investigated and found that this woman has a wound in her womb; for every time she urinates she suffers severe pain. Occasionally, but not always, she finds blood in her urine; but no blood is found immediately after urination, neither upon wiping herself nor on the "examining rag". I, therefore, agree with you that this woman is permitted to cohabit with her husband, for, when a woman says she has a wound in her womb from which the blood exudes, she is to be believed.
This responsum is addressed to Rabbi Yekutiel; the Mordecai Hagadol, however, ascribes the question to Rabbi Asher.
SOURCES: Am II, 52; Mordecai Hagadol, p. 339a.