(כב) וְכִֽי־יִנָּצ֣וּ אֲנָשִׁ֗ים וְנָ֨גְפ֜וּ אִשָּׁ֤ה הָרָה֙ וְיָצְא֣וּ יְלָדֶ֔יהָ וְלֹ֥א יִהְיֶ֖ה אָס֑וֹן עָנ֣וֹשׁ יֵעָנֵ֗שׁ כַּֽאֲשֶׁ֨ר יָשִׁ֤ית עָלָיו֙ בַּ֣עַל הָֽאִשָּׁ֔ה וְנָתַ֖ן בִּפְלִלִֽים׃ (כג) וְאִם־אָס֖וֹן יִהְיֶ֑ה וְנָתַתָּ֥ה נֶ֖פֶשׁ תַּ֥חַת נָֽפֶשׁ׃
(22) When men fight, and one of them pushes a pregnant woman and a miscarriage results, but no other damage ensues, the one responsible shall be fined according as the woman’s husband may exact from him, the payment to be based on reckoning. (23) But if other damage ensues, the penalty shall be life for life,
Septuagint Exodus 21:22-23
And if two men strive and smite a woman with child, and her child be born imperfectly formed, he shall be forced to pay a penalty; as the woman’s husband may lay upon him, he shall pay with a valuation. But if it be perfectly formed he shall give life for life.
The Greek translators of the Bible translated "ason" as "exeikonismenon" which literally translates as "from the image," invoking the notion of "betzelem elohim"--human beings were created in God's image. The translator may have translated in this way due to the similarity between the Hebrew "ason" and the Greek "soma" meaning human life. Thinking the word meant "human life" the translator shifted it to a more theologically evocative word.
Aristotle, The History of Animals, Book VII, Part 6
In the case of male children the first movement usually occurs on the right-hand side of the womb and about the fortieth day, but if the child be a female then on the left-hand side and about the ninetieth day. However, we must by no means assume this to be an accurate statement of fact, for there are many exceptions...
About this period the embryo begins to resolve into distinct parts, it having hitherto consisted of a flesh-like substance without distinction of parts.
Philo, The Special Laws 111.108-109
But if anyone has a contest with a woman who is pregnant, and strike her a blow on the belly, and she miscarry, if the child was conceived within her is still unfashioned and unformed, he shall be punished by a fine.... But if the child which was conceived had assumed a distinct shape in all its parts, having received all its proper connective and distinctive qualities, he shall die; for such a creature as that is a man, whom he has slain while still in the workshop of nature, who had not thought it as yet a proper time to produce him to the light, but had kept him like a statue lying in a sculptor’s workshop, requiring nothing more than to be released and set out into the world.
Philo, On the Virtues
137) But the law banishes to a distance from the sacred precincts all animals which are pregnant, not permitting them to be sacrificed until they have brought forth, looking on the animals which are still in the womb as equal to what has just been born... for it is the most impious of all customs, to slay both offspring and mother at one time and on one day. (139) And it appears to me that some lawgivers, having started from this point, have also promulgated the law about condemned women, which commands that pregnant women, if they have committed any offence worthy of death, shall nevertheless not be executed until they have brought forth, in order that the creature in their womb may not be slain with them when they are put to death.
Temple Scroll 52
And you shall not slaughter a cow or a ewe and its young on the same day, and you shall not kill a mother with its young.
Sifre Zuta to Numbers 35:22
I might have thought that if she were pregnant they would postpone [the execution] until she gave birth. Therefore, the Torah teaches, “He that smote him shall surely be put to death.” I might have thought that if she were three months pregnant, they should not postpone [the execution] until she gives birth; but if she were nine months pregnant, they should postpone [the execution] until she has given birth. Therefore, Scripture teaches, “He shall surely be put to death.”
(א) בְּהֵמָה הַמַּקְשָׁה לֵילֵד, וְהוֹצִיא הָעֻבָּר אֶת יָדוֹ וְהֶחֱזִירָהּ, מֻתָּר בַּאֲכִילָה. הוֹצִיא אֶת רֹאשׁוֹ, אַף עַל פִּי שֶׁהֱחֱזִירוֹ, הֲרֵי זֶה כְיָלוּד.
(1) [If] an animal has difficulty giving birth, and the fetus protruded its fore-leg and withdrew it, [the fetus] is permitted for eating. [If] it protruded its head, even if it withdrew it, it is as if it were born.
משום רבי ישמעאל אמרו אף על העוברין מאי טעמיה דרבי ישמעאל דכתיב (בראשית ט, ו) שופך דם האדם באדם דמו ישפך איזהו אדם שהוא באדם הוי אומר זה עובר שבמעי אמו
The Sages said in the name of Rabbi Yishmael: A descendant of Noah is executed even for killing fetuses. What is the reason for Rabbi Yishmael? It is written: “One who sheds the blood of a person, by a person [ba’adam] his blood shall be shed” (Genesis 9:6). The word ba’adam literally means: In a person, and is interpreted homiletically: What is a person that is in a person? You must say: This is a fetus that is in its mother’s womb.
Josephus Contra Apion ii.202
The law enjoins us to bring up all our offspring, and forbids women to cause abortion of what is begotten, or to destroy it afterward. If any woman appears to have done so, she will be a murderer of her child, by destroying a living creature and diminishing human kind.
The Didache 2:1-2
Now the second command of the teaching: Thou shalt not kill…Thou shalt not murder the child in the mother’s womb nor kill the newly born.
(ו) הָאִשָּׁה שֶׁהִיא מַקְשָׁה לֵילֵד, מְחַתְּכִין אֶת הַוָּלָד בְּמֵעֶיהָ וּמוֹצִיאִין אוֹתוֹ אֵבָרִים אֵבָרִים, מִפְּנֵי שֶׁחַיֶּיהָ קוֹדְמִין לְחַיָּיו. יָצָא רֻבּוֹ, אֵין נוֹגְעִין בּוֹ, שֶׁאֵין דּוֹחִין נֶפֶשׁ מִפְּנֵי נָפֶשׁ:
(6) A woman who was having trouble giving birth, they cut up the fetus inside her and take it out limb by limb, because her life comes before its life. If most of it had come out already they do not touch it because we do not push off one life for another.
Tertullian, On the Soul
Consider the wombs of the most sainted women instinct with the life within them, and their babes which not only breathed therein, but were even endowed with prophetic intuition. See how the bowels of Rebecca are disquieted, Genesis 25:22-23 though her child-bearing is as yet remote, and there is no impulse of (vital) air. Behold, a twin offspring chafes within the mother's womb, although she has no sign as yet of the twofold nation....
Accordingly you read the word of God which was spoken to Jeremiah, Before I formed you in the belly, I knew you. Jeremiah 1:5 Since God forms us in the womb, He also breathes upon us, as He also did at the first creation, when the Lord God formed man, and breathed into him the breath of life. Genesis 2:7 Nor could God have known man in the womb, except in his entire nature: And before you came forth out of the womb, I sanctified you. Well, was it then a dead body at that early stage? Certainly not. For God is not the God of the dead, but of the living.
Basil, 4th Century Bishop, Cappadocia, Letter 188
II. The woman who purposely destroys her unborn child is guilty of murder. With us there is no nice enquiry as to its being formed or unformed. In this case it is not only the being about to be born who is vindicated, but the woman in her attack upon herself; because in most cases women who make such attempts die. The destruction of the embryo is an additional crime, a second murder, at all events if we regard it as done with intent. The punishment, however, of these women should not be for life, but for the term of ten years. And let their treatment depend not on mere lapse of time, but on the character of their repentance.
its head came out: With a woman that is experiencing difficulty giving birth and is in [mortal] danger. And it is taught in the first section [of this teaching], "the midwife extends her hand and cuts it up and extracts [the pieces];" as the entire time that that it has not gone out into the air of the world, it is not [considered] a soul (nefesh) and [so] it is possible to kill it and to save its mother. But when its head came out, we cannot touch it to kill it, as it is like a born [baby]; and we do not push off one soul for the sake of another.
(ט) אַף זוֹ מִצְוַת לֹא תַּעֲשֶׂה שֶׁלֹּא לָחוּס עַל נֶפֶשׁ הָרוֹדֵף. לְפִיכָךְ הוֹרוּ חֲכָמִים שֶׁהָעֻבָּרָה שֶׁהִיא מַקְשָׁה לֵילֵד מֻתָּר לַחְתֹּךְ הָעֵבָּר בְּמֵעֶיהָ בֵּין בְּסַם בֵּין בְּיָד מִפְּנֵי שֶׁהוּא כְּרוֹדֵף אַחֲרֶיהָ לְהָרְגָהּ. וְאִם מִשֶּׁהוֹצִיא רֹאשׁוֹ אֵין נוֹגְעִין בּוֹ שֶׁאֵין דּוֹחִין נֶפֶשׁ מִפְּנֵי נֶפֶשׁ וְזֶהוּ טִבְעוֹ שֶׁל עוֹלָם:
(9) This, indeed, is one of the negative mitzvot - not to take pity on the life of a pursuer (rodef). On this basis, our Sages ruled that when complications arise and a pregnant woman cannot give birth, it is permitted to abort the fetus in her womb, whether with a knife or with drugs. For the fetus is considered a rodef of its mother. If the head of the fetus emerges, it should not be touched, because one life should not be sacrificed for another. Although the mother may die, this is the nature of the world.
ליכא מידעם דלישראל שרי בדבר - ...ועל העוברים דעובד כוכבים חייב וישראל פטור אע"ג דפטור מ"מ לא שרי...מיהו קשה דאמרינן בפרק בן סורר ומורה (לקמן סנהדרין דף עב:) יצא ראשו אין נוגעין בו דאין דוחין נפש מפני נפש אבל קודם שיצא ראשו החי' פושטת ידה וחתכתו לאברים ומוציאה כדי להציל את אמו וכה"ג בעובד כוכבים אסור כיון שהוזהרו על העוברים וי"ל דהא נמי בישראל מצוה כדי להציל ואפשר דאפילו בעובד כוכבים שרי:
There is nothing which is permitted to a Jew but prohibited to a non-Jew:...Concerning killing a fetus, a Gentile is liable but a Jew is exempt. But even though he is exempt, it is still not permitted. However, there is a difficulty for it says in Sanhedrin 72b, "if its head emerges, one may not touch it for the life of one may not be set aside for the life of another." But before its head emerges, the midwife may put her hand in the womb and cut it out limb by limb in order to save the mother. But this is not permitted to a Gentile, for they are liable for killing fetuses. And we can answer that it is a mitzvah for the Jew to save the mother and this might even be so for a Gentile.