Although abortion is prohibited for both Jews and Noaḥides (i.e., non-Jews, who are obligated in the seven Noaḥide laws), there is a difference when it comes to punishment. A Jew who kills a fetus is not punished by a beit din for doing so, while a gentile who kills a fetus is liable for the death penalty.
As is well known, non-Jews are obligated in seven mitzvot. A non-Jew who transgresses any of them incurs the death penalty. One of these seven is the prohibition against murder, as Noaḥ was told, upon exiting the ark: “Whoever sheds the blood of a person (ha-adam), by a person (ba-adam) shall his blood be shed, for God made people in His image” (Bereishit 9:6). R. Yishmael extrapolates that even a person who kills a fetus incurs the death penalty, as the verse can be read homiletically: “Whoever sheds the blood of a person (ha-adam) in a person (ba-adam) – his blood shall be shed.” Who is a person in a person? A fetus (Sanhedrin 57b; MT, Laws of Kings 9:4).
In contrast, a Jew who kills a fetus does not incur the death penalty. When the Torah later explains that a murderer is put to death, it does not hint that a fetus-killer would be included in this category. Nevertheless, it is clear that a Jew may not kill a fetus, as there is a general principle that anything forbidden to non-Jews is forbidden to Jews as well. The purpose of the Torah is to sanctify the Jewish people and to demand much of them when it comes to mitzvot, so it is inconceivable that something forbidden to non-Jews would be permissible for Jews (Sanhedrin 59a). Thus, once we know that a non-Jews may not kill a fetus, it follows that Jews may not, either. The only distinction is in the severity of the punishment: a non-Jew is put to death for killing a fetus, while a Jew is not.
It is important to know that according to halakha, even when a beit din had the authority to apply capital punishment, only very rarely was a Torah-mandated execution carried out. It was so rare that a Sanhedrin which executed one person in seven years was labeled “destructive.” According to R. Elazar b. Azarya, even if it executed only one person in seventy years, it was considered a destructive Sanhedrin (m. Makkot 1:10). Although there are dozens of sins for which the Torah mandates capital punishment, in practice the beit din did not kill a single person in seven (or seventy) years. Thus, we see that the death penalty prescribed by the Torah, whether for Jews or non-Jews, was intended mainly as a deterrent and to express the severity of the sin and its punishment in this world and the next. It was not meant to lead to frequent executions.
In theory, then, in the matter of abortion, the Torah was more stringent for non-Jews than for Jews. This may be because many gentile nations tend to devalue human life, to the extent that some are suspected of bloodshed (m. Avoda Zara 2:1). In order to make it clear that their attitude is completely wrong, the Torah makes abortion a capital crime for them. Nevertheless, it would seem that when it comes to abortion necessitated by severe illness, the law for Jews and non-Jews is the same; in any situation where Jews may terminate a pregnancy, non-Jews may, too.
. As we will see, according to many poskim, a Jewish woman may undergo an abortion if the fetus suffers from a severe illness or if there is a concern that continuing the pregnancy will cause the mother to become gravely ill. Some say that it is forbidden for non-Jews to undergo abortions in such cases, since the prohibition of abortion is more severe for them. However, it seems that in practice, in any case in which a Jewish woman would be permitted to terminate a pregnancy, a non-Jewish woman would be permitted to do so as well. This is based on the fundamental principle that there is nothing forbidden to a non-Jew but permitted to a Jew. True, the Torah was more stringent regarding the theoretical punishment for non-Jews, but that was only in order to deter them from sinning, as emerges from the second explanation of Tosafot to Sanhedrin 59a, s.v. “leika.”
So far, we have been assuming that the principle mentioned above – that there can be nothing permitted to Jews but forbidden to non-Jews – is halakhically binding (Tosafot on Ḥullin 33a, s.v. “eḥad”). In contrast, some Aḥaronim write that according to Rambam, this principle is not halakhically binding. Therefore, it is possible that something is prohibited for a non-Jew but permissible for a Jew, such as eating meat from an animal that is still twitching after being slaughtered (MT, Laws of Kings 9:13; Ḥatam Sofer, YD §19; Arukh La-ner to Sanhedrin 59a).
However, it seems that all opinions agree with the principle in general, as we find numerous poskim who take it into account. The Aḥaronim who seem to reject the principle mean that even though Jews are required to be stringent, there may be a leniency in some minor detail. For example, Jews must be meticulous in following all the laws of sheḥita (animal slaughter), but as a result, once the animal has been properly slaughtered, even if it is still twitching, eating its meat is not considered a transgression of ever min ha-ḥai (eating part of a living animal) for a Jew, whereas itis forbidden to a non-Jew. Therefore, there cannot be any law which is fundamentally stricter for non-Jews than for Jews, and certainly not an issue as morally and practically important as abortion. See also Rashba to Ḥullin 33a, who states that when there is a rationale, a specific detail might be more lenient for Jews. See also Sdei Ḥemed, Klalei Ha-Mem 166.
Thus, the prohibition of abortion must be the same for both Jews and non-Jews, the sole difference being the punishment specified by the Torah. There is another difference between Jews and non-Jews in the requirement for meting out punishment. If a non-Jew transgresses one of his seven mitzvot, he can be executed even based on the testimony of one witness, and even if he was not warned about the punishment for his action before he transgressed. In contrast, a Jew can be executed only based on the testimony of two witnesses, and only after being warned. This does not mean that the Torah requires us to pursue every non-Jew who transgressed one of the seven Noaḥide commandments in order to execute him. Rather, when necessary for the sake of improving the world, the legal system may execute a Noaḥide sinner, even based on the testimony of one witness, and even if he has not been warned.