Gemarah

(Abaye): Bar Pada agrees that Hekdesh of a fetus in a Tam mother takes effect. They argue about Hekdesh of a fetus in a Ba'al Mum;

Bar Pada holds that since the mother does not get Kedushas ha'Guf, the fetus gets only Kedushas Damim;

R. Yochanan holds that Ubar Lav Yerech Imo. Even though the mother does not get Kedushas ha'Guf, the fetus does.

25a (R. Yochanan): If one was Makdish a pregnant animal for a Chatas and it gave birth, he may bring either of them for his Chatas.

He holds that Ubar Lav Yerech Imo (a fetus is not considered like a limb of the mother, rather, like an independent animal). It is as if he was Makdish two Chata'os for Acharayus. He may offer either for Kaparah.

Question (Beraisa): If one (gave a document of freedom, and) said to his pregnant Shifchah "you are (still) a slave, and your fetus is free", she acquires freedom on behalf of her child.

If Ubar Lav Yerech Imo, how can she acquire for her child?!

(Beraisa): A slave cannot acquire freedom for another slave of his own master.

R. Yochanan is refuted.

Suggestion: Tana'im argue about this.

Bava Kama 47a (Rava): If a pregnant cow damaged, one may collect from the calf.

This is because Ubar Yerech Imo.

Sanhedrin 80a (Beraisa): If a cow gored and gave birth before it was sentenced, the calf is permitted.

Inference: This is even if the cow was pregnant with the calf at the time of the goring!

Question: Rava disqualifies (for Korbanos) the calf of a cow that gored or was Nirva (a man had Bi'ah with it). Also the calf was party to the goring or bestiality!

Answer #1 - Correction (Beraisa): Rather, if it gave birth before it was sentenced, the calf is permitted, but not if it became pregnant and gave birth after it was sentenced.

Question: One opinion permits Zeh v'Zeh Gorem (something that results from two causes, one of which is forbidden). How can he answer?

Answer #2 (Ravina): If it gave birth before it was sentenced, the calf is permitted, but not if it was sentenced while pregnant, for Ubar Yerech Imo (it was sentenced with its mother).

(Mishnah - R. Eliezer): The offspring of a Tereifah is Pasul (for a Korban);

R. Yehoshua says, it is Kosher.

(Rav Acha): They argue about a Terefah animal that became pregnant. R. Eliezer forbids Zeh v'Zeh Gorem, and R. Yehoshua permits.

(Ravina): They argue about a pregnant animal that became Tereifah. R. Eliezer holds that Ubar Yerech Imo, and R. Yehoshua disagrees. (Rav Acha holds that a Tereifah can give birth; Ravina disagrees.)

Erchin 7a (Mishnah): If a woman about to be executed sat on the Mashber (birthing stool), we wait for her to give birth.

Once the fetus starts to leave, it is considered a separate entity.

(Rav Nachman): If a woman sat on the Mashber and died on Shabbos, we bring a knife, cut her open and remove the fetus (perhaps it will live).

(Rabah): He permits bringing a knife through a Reshus ha'Rabim.

A Mishnah permits Chilul Shabbos for Safek Piku'ach Nefesh (saving a life). One might have thought that this is only when there is a Chazakah (that a Yisrael was alive. Here, the fetus is a Nefel!)

Chulin 75a (R. Ami): If one slaughters a Terefah and finds a full term fetus inside, R. Meir permits this fetus through Shechitah. Chachamim disagree.

(Rava): All permit it through its own Shechitah. The Torah permits a fetus through Shechitah of its mother (if she is Kosher) or through its own Shechitah.

Rishonim

Rosh (Yoma 8:13): Bahag says that if we know that if a pregnant woman will miscarry if she does not eat on Yom Kipur, even though perhaps the fetus is a Nefel, we feed her. The Ramban infers that we are Mechalel for the fetus, even if there is no danger to her, like it says in Erchin. Some disagree; she may eat due to danger to her. It is dangerous to miscarry. We permit when a woman sat on the Mashber and died, for it is as if the baby was born. We no longer say that Ubar Yerech Imo. He does not depend on her. He is alive, just a door is locked in front of him.

Question (Tosfos Sanhedrin 80b DH Ubar): Our Gemara explained according to the opinion that Ubar Yerech Imo. It did not ask about the opinion that Ubar Lav Yerech Imo. This shows that the Halachah is Ubar Yerech Imo. Perhaps our Gemara merely sought to answer for Rava. However, we can learn from him! In Chulin, we say that the Tana'im argue about Ubar Yerech Imo according to the opinion than a Tereifah cannot give birth, and this is the Halachah. The Halachah follows R. Yehoshua (who says that Ubar Lav Yerech Imo), for R. Eliezer is from Beis Shamai. In Beitzah, the Gemara discusses the child of a Tereifah! And Rava himself (75a) permits a fetus found in a slaughtered Terefah mother, through its own Shechitah!

Answer #1 (Tosfos and Rosh Bava Kama 5:2): Ubar Yerech Imo in every respect, except for Tereifah. Since it has its own life, we do not say that it became Tereifah along with its mother.

Tosfos (ibid.): In Temurah, the Gemara refuted R. Yochanan, then suggested that Tana'im argue about his law. The Gemara often says that Ploni is refuted, even though we could say that some Tana'im hold like him, when Ploni's opinion is not primary. We challenged Rava (who says that Tevilah of a pregnant woman for conversion) from R. Yochanan (who says that we count generations of Mitriyim from the father, because Ubar Lav Yerech Imo - Yevamos 78a), i.e. just to show that all agree with Rava's law.

Answer #2 (Tosfos, citing Rav R. Tam): Everywhere, the Halachah is Ubar Lav Yerech Imo. The text in Temurah should not say that R. Yochanan was refuted. Rava says that sentence passed on a pregnant animal applies also to the fetus, for until now its life depended on its mother, but not because Ubar Yerech Imo. Likewise, we do not wait for a woman to give birth before executing her. However, why does Rava permit collecting from the calf to pay for the mother's share of the damage, unless we say Ubar Yerech Imo?!

Tosfos (Bava Kama 47a DH Mai): Rava forbids (for a Korban) a fetus in a mother that was Nirva or killed. This does not prove that Ubar Yerech Imo. There, also it benefited from the Bi'ah, or helped to kill!

Note: Seemingly, if the bestiality was only Ha'ara'ah (the initial stage of Bi'ah) the fetus does not benefit. If the animal killed through biting, the fetus did had no part in this. Perhaps the Torah always forbids, because in most cases the fetus benefits or helped to kill.

Tosfos (ibid.): However, since Rava says that the calf pays for the mother's share of the damage, he must hold that Ubar Yerech Imo. If two Tam animals damaged, one cannot collect from one what the other should pay!

Poskim

Shulchan Aruch (OC 330:5): If a pregnant woman sat on the Mashber and died on Shabbos, we bring a knife even through Reshus ha'Rabim, cut her open and remove the fetus. Perhaps it is alive.

Shulchan Aruch (7): We are not Mechalel Shabbos for an eight-month baby (a Nefel), or a Safek whether it is a seven or eight month baby, unless his hair and fingernails are finished.

Magen Avraham (15): Olas Shabbos asked that in Sa'if 5, even if we are unsure whether the fetus was ever alive, we are Mechalel Shabbos for it. Why is here different? Above, we know that the months of pregnancy were finished. This depends on what the Rosh and Ran (Yoma 3b DH v'Chasuv) wrote about a pregnant woman who smelled (food on Yom Kipur - 82a). If she does not eat, the fetus will die. Even though it is a Safek Nefel, we feed her. He brings a proof from Erchin 7a, which says that we are Mechalel Shabbos for a Safek. The Ramban says that we are not Mechalel Shabbos for Nefalim. In Erchin, the fetus is considered born. It is no longer Yerech Imo, since she died. It is alive, and a door is locked in front of it. The only concern is that it does not have Chezkas Chayim.

Note: The Ramban is in Toras ha'Adam (Inyan ha'Sakanah, DH uv'Hilchos, p.28-29 in Kisei ha'Ramban Volume 2). First he brings from Bahag that we are Mechalel Shabbos for a fetus, for perhaps it will observe many Shabbosos. This applies even within 40 days of conception, when it has no life of its own. Then the Ramban cites an opposing opinion. He concludes 'we are lenient about Safek Nefashos'.

Magen Avraham: It seems that the Ramban requires that we know that the months of pregnancy were finished, even if she sat on the Mashber, since he brings a proof from the Heter to kill him (if the mother is in mortal danger due to birth). The Ran says that since we see that his hair and fingernails are not finished, we are concerned due to Safek.

Shulchan Aruch (YD 14:6): If one stuck his hand inside an animal's womb and cut part of the fetus and did not remove it, and later slaughtered the mother, (even) that piece of the fetus is permitted, since it did not leave.

Rema: If one slaughtered the fetus in the womb, this is not called Shechitah.

R. Akiva Eiger: If the mother died and then he slaughtered the fetus inside, it seems that this is Shechitah. The Gemara (Chulin 74a) asked only about Shechitah inside a live mother. Then we can say that the fetus is like part of the mother, and it is not a separate animal. This is like the Magen Avraham brings from the Ramban. Even though a Yisrael is not killed for killing a fetus, if the mother died, it is as if the baby was born. However, the Levush forbids due to Chaladah (the knife is covered at the time of Shechitah). This disqualifies also if the mother died.

Shulchan Aruch (OC 605:1): We take two chickens for a pregnant women (for Kaparos), for perhaps she will gave birth to a male.

Gra (DH v'Lokchin): We hold that Ubar Yerech Imo. R. Yochanan holds that Ubar Lav Yerech Imo, and he was refuted. The Sugyos in Gitin, Bava Kama and Erchin hold that Ubar Lav Yerech Imo. The Rosh (Bava Kama 5:2) rules like this, unlike the Ro'oh and R. Tam.

Question: The Gemara says that if Ubar Yerech Imo, if the mother was Nirva, also the fetus was Nirva. If so, why may one have Bi'ah with his wife when she is pregnant? (Perhaps the fetus is a girl, and) it is as if he has Bi'ah also with his daughter! Even though Bi'ah with a girl less than three years old is not considered Bi'ah, presumably we forbid mid'Rabanan, just like Bi'ah with a boy less than nine years old.

Note: Likewise, if we assume that the fetus is a boy, the Isur mid'Rabanan of Bi'ah with a boy less than nine should apply! Perhaps the questioner showed that we cannot be lenient due to a Safek mid'Rabanan (perhaps the fetus is a girl), for we should forbid mid'Rabanan also for girls less than three.

Answer (R. Akiva Eiger Teshuvah 1:172): One may not have Bi'ah with a girl less than three because it is not called Bi'ah, therefore this is like spilling seed on rocks. See Nimukei Yosef (Yevamos 19a). If she is three, it is called Bi'ah, even though she cannot become pregnant and give birth. Therefore, Chachamim did not need to decree about Ervah below three years. Regarding a pregnant woman, there is no concern for wasting seed, therefore it is permitted even mid'Rabanan.