The Gemara says yevomos 12:2 that R. Bivi said before R. Nachman: 3 women Mishamshos Bemuch: Ketana, Meuberes, and Meinika. The reason is lest she becomes pregnant...
My question is: in Maseches Niddah 27:1 the Gemara disproves R. Menachem for saying that a woman can become pregnant during a pregnancy by asking "Veha Omar Mar a woman does not become pregnant Vechozeres and become pregnant. So why:
1) In Maseches Niddah do they not bring the Gemara in Yevomos as a Tana that supports R. Menachem?
2) In Yevomos do they not ask against R. Bivi from the Omar Mar in Niddah?
Meir Zirkind, Weston FL USA
Your question is asked by Tosfos to Yevamos 12b, DH Shema. Baruch she'Kivanta!
1. Tosfos answers that when the Gemara in Nidah (27a) states that a woman does not become pregnant and then become pregnant again, this means that she cannot become "re-pregnant" with a viable baby. However, it is possible for her to become pregnant with a baby which will not survive.
2. The Me'iri in Yevamos answers that the Gemara here does not mean that the woman might actually become pregnant again. Rather, the worry is that the semen may cover over the embryo, damage it, and transform it into a "Sandal." Even though there is no concern that she will become pregnant with a different child since a woman cannot become pregnant twice in this way, nevertheless sometimes a substance can be created which covers over the fetus.
3. An alternative explanation is given by Rabeinu Tam, cited by Tosfos here. He also says that the woman does not become "re-pregnant." Rabeinu Tam writes that our Gemara is referring to a woman pregnant with twins. If she does not use a "Moch," the semen may force its way through between the two fetuses and as a result of this pressure one of the twins will be made into a "Sandal."
Kol Tuv,
Dovid Bloom