Responsa for Niddah 41:45

קשתה שנים ולשלישי הפילה ואינה יודעת מה הפילה

— Rather, explained R. Nahman b. Isaac: The point at issue between them<span class="x" onmousemove="('comment',' R. Judah and the Rabbis. ');">³⁸</span> is the question whether it is possible for the uterus<span class="x" onmousemove="('comment',' Lit., 'grave'. ');">³⁹</span> to open<span class="x" onmousemove="('comment',' When an embryo or any other object passes out. ');">⁴⁰</span> without bleeding.<span class="x" onmousemove="('comment',' Blood of labour. Both R. Judah and the Rabbis regard the shapeless object as a piece of flesh, and not as a mass of congealed blood. Hence whatever its colour the woman cannot be regarded as a menstruant. R. Judah, however, maintains that the uterus never opens without some bleeding though this may sometimes escape observation. The woman is, therefore, unclean on account of the inevitable discharge of the blood of labour even though the object was green or white and no blood whatsoever had been observed. The Rabbis, on the other hand, maintain that the uterus sometimes opens without any accompanying bleeding and the woman is, therefore, clean whenever no discharge is observed. ');">⁴¹</span> They<span class="x" onmousemove="('comment',' R. Judah and the Rabbis. ');">³⁸</span> thus differ on the same principle as that on which the following Tannas differ. For it was taught: If a woman was in hard labour for two days<span class="x" onmousemove="('comment',' Within the eleven days' period intervening between the menstrual periods. ');">⁴²</span> and on the third she aborted and<span class="x" onmousemove="('comment',' Besides being uncertain whether the abortion was accompanied by bleeding. ');">⁴³</span> does not know what she had aborted<span class="x" onmousemove="('comment',' Sc. whether it was an embryo or a mere lump of flesh. ');">⁴⁴</span>

Teshuvot Maharam