Talmud - Yevamot 12b יבמות י״ב ב׳

And the halakha is that the rival wife of an aylonit is permitted, and this is the case even if her first husband knew of her status and her marriage was fully valid. The mitzva of levirate marriage does not apply to an aylonit, but her rival wife is not forbidden. And even in the case of the rival wife of his aylonit daughter who was recognized as such, the other wife is not considered the rival wife of a forbidden relative.

The Gemara asks: However, with regard to that which the mishna teaches: Were found to be, from which it was inferred that there is a difference between an aylonit whose condition was known by the husband beforehand and one who was recognized by him only later, how is this to be explained? The Gemara answers that one should emend this and teach simply: That were, and not: Were found to be. When Ravin came from Eretz Yisrael he said that Rabbi Yoḥanan said: There is one halakha with regard to the rival wife of a girl who refused her husband, and the rival wife of an aylonit, and also the rival wife of one who remarries his divorcée: They are all permitted.

§ Incidental to the case of refusal, the Gemara cites a related halakha. Rav Beivai taught a baraita before Rav Naḥman: Three women may engage in relations with a contraceptive resorbent, a soft fabric placed at the entrance to their wombs to prevent conception, despite the fact that this practice is generally prohibited. They are as follows: A minor, a woman who is already pregnant, and a nursing woman. The baraita specifies the reason for each exception: A minor may do so lest she become pregnant and perhaps die; a pregnant woman, lest she be impregnated a second time and her previous fetus becomes deformed into the shape of a sandal fish by being squashed by the pressure of the second fetus. As for a nursing woman, she does so lest she become pregnant and her milk dry up, in which case she will wean her son too early, thereby endangering him, and he will die.

And the baraita continues: Who is considered a minor? It is a girl from the age of eleven years and one day until the age of twelve years and one day. If she was younger than this or older than this, she may go ahead and engage in relations in her usual manner. This is the statement of Rabbi Meir. Since it is assumed that a minor who is less than eleven years old cannot become pregnant, she is considered to be in no danger. And the Rabbis say: Both this one and that one, i.e., in all these cases, she may go ahead and engage in relations in her usual manner, and Heaven will have mercy upon her and prevent any mishap, since it is stated: “The Lord preserves the simple” (Psalms 116:2).

The Gemara analyzes the baraita: From the fact that the baraita states: Lest she become pregnant and perhaps die, this indicates by inference that there is a minor who can become pregnant and will not die, although the conditions for this scenario of a minor giving birth and surviving are unclear. If so, that a minor might be impregnated and give birth, we find the case of one’s mother-in-law who refused her husband. Since it is possible for a woman to give birth to a daughter while still a minor, if a man betroths this daughter while still an infant, the mother might be a mother-in-law who performed refusal.

And yet we learned in the mishna: You cannot say, i.e., the possibility does not exist, in the case of his mother-in-law, his mother-in-law’s mother, and his father-in-law’s mother, that they were found to be an aylonit or performed refusal, as refusal may be performed only by a minor, who cannot give birth. If so, there is apparently a contradiction between the mishna and the baraita. The Gemara answers: Do not say: Lest she become pregnant and perhaps die, which indicates that it is possible for her not to die from the impregnation. Rather, say: Lest she become pregnant and die. In other words, although it is uncertain whether she will be impregnated, if she does become pregnant she will certainly die, which means that there is no case in which a minor could give birth and live.

As Rabba bar Livai said: There is a limit with regard to her pregnancy, i.e., that of a young girl. Before this time, the age of eleven, she cannot be impregnated at all. During this time, from age eleven to twelve, she dies and her fetus dies. After this time, from twelve onward, she lives and her fetus lives.

The Gemara raises a difficulty: Is that so? But didn’t Rabba bar Shmuel teach: You cannot say in the case of his mother-in-law, and his mother-in-law’s mother, and his father-in-law’s mother that they were found to be an aylonit or performed refusal, as they already gave birth. This indicates that a minor can give birth, as otherwise he should have stated: As they are already mature. Rather, actually, the original version of the baraita is correct: Lest she become pregnant and perhaps die. But this is difficult with regard to the mishna, which indicates that this scenario is impossible.

Rav Safra said: Children are equivalent to signs of puberty. In other words, a girl who gives birth does not retain the legal status of a minor, as the very fact that she bore children is equivalent to a physical sign of maturity, usually in the form of pubic hairs. And some say: Children are preferable to signs of puberty. The Gemara asks: What is the practical difference that arises from the question of whether bearing children is equivalent or preferable to signs of maturity? The Gemara answers: The difference is that even according to the opinion of Rabbi Yehuda, who said that a minor may perform refusal even after she develops two pubic hairs, until the black hairs of her genitals are more plentiful than the hairless skin, in the case of children he concedes that she is considered mature and may not perform refusal.

Traduction : The William Davidson digital edition of the Koren Noé Talmud, with commentary by Rabbi Adin Even-Israel Steinsaltz.

Yevamot 12b examines levirate marriage exemptions for an aylonit and her co-wife, then discusses three women permitted to use contraception.