A Mother’s Obligation to Her Fetus (Column 562)

With God’s help

Disclaimer: This post was translated from Hebrew using AI (ChatGPT 5 Thinking), so there may be inaccuracies or nuances lost. If something seems unclear, please refer to the Hebrew original or contact us for clarification.

A few days ago a friend referred the following question to me:

A woman in labor has declared that she absolutely refuses to undergo a Caesarean section. There is no risk to her life. However, the doctors have concluded that if she is not operated on, there is a risk to the fetus’s life or that the child will be born with a disability. Is a physician permitted to operate on her? [This is, nowadays, a real-life dilemma in hospitals.]

Is there a direct answer to this, or one by way of analogy?

This is a fascinating question, and I responded to him briefly with my view. Here I wish to expand on it a bit.

Point of Departure: One may not harm one person in order to save another

As a rule, no one is permitted to harm one person in order to save another. When it comes to killing one person to save another, this is an explicit prohibition in the Talmud grounded in the reasoning: “Why do you see your blood as redder—perhaps that man’s blood is redder?” (Pesachim 25b and parallels). One is not authorized to prefer Reuven’s blood over Shimon’s, and therefore a person may not kill Shimon to save Reuven. This is the ruling of “be killed rather than transgress” regarding murder.

By reasoning, the same should apply to non-lethal harm to Shimon in order to save Reuven. For example, if Reuven needs a kidney to survive, no one is permitted to take a kidney from Shimon without his consent in order to transplant it into Reuven, even though Shimon will continue to live a reasonable life with one kidney. Note that at first glance one might claim that removing a kidney is an act of battery (“chovel”), and seemingly that prohibition is set aside for the sake of saving a life (pikuach nefesh), like all Torah prohibitions except for the three cardinal sins. And yet, as far as I know, the halakhic decisors unanimously agree that one may not do this—each for his own reasons.

To explain this, some rely on a technical consideration: why take from Shimon and not from Levi? Shimon does not owe Reuven any more than anyone else in the world, and therefore he may refuse the request for his kidney, arguing that they should look for someone else. Of course, anyone else can refuse on the same grounds—“go here and he rejects you; go there and he rejects you.” Technically these arguments can be accepted, but it is doubtful there is a substantive claim here. In principle, no one has a genuine right not to donate a kidney, and so I would expect them to conduct a fair lottery among all compatible donors. Others invoke the logic of “what difference is there between complete killing and partial killing,” i.e., that removing an organ is a kind of partial homicide (see Bava Kamma 65a; Bava Metzia 95a), and just as it is forbidden to kill Shimon to save Reuven, so too it is forbidden to injure him. Still, the precise halakhic explanation is unclear, for the prohibition of battery is not the prohibition of murder. Moreover, halakhah rules that if a pursuer (rodef) can be stopped by injuring him, one must do so, and one is not permitted to kill him (“he can be saved by one of his limbs”). Perhaps one could say this is a “light murder,” but it is more reasonable to conclude from here that injury is not murder.

In my understanding, the matter is more fundamental (see my article on duties and rights in halakhah and Column 291): just as one may not kill Shimon to save Reuven, so too one may not harm him or his property to save Reuven. More broadly: any violation of Shimon’s rights in order to save Reuven is forbidden. Regarding damage to property, this is Rashi’s position in Bava Kamma 60b, that a person may not save himself with his fellow’s property. In that column I noted that other Rishonim and Acharonim agree in principle, though they reject ruling this way in practice for technical reasons. There I also cited that the author of Binyan Tzion, in several responsa dedicated to the matter, extends Rashi’s view to any infringement of Shimon’s rights (he attributes it to any interpersonal prohibition, but it is clear the reference is to violations of rights, not every interpersonal sin). I explained there that the stringency in such cases is not due to the severity of the prohibition but to its nature. Violating a person’s right is not one of the three cardinal sins; thus, its precedence over pikuach nefesh is not because it is a more severe prohibition. For this reason, it is not listed among the three cardinal sins (which are listed there only because they override pikuach nefesh on account of their severity). Infringing another’s rights overrides pikuach nefesh because no one is authorized to enter another’s “territory” and decide on his behalf—even if the prohibition entailed is relatively light compared to pikuach nefesh. Even if it is proper to be harmed to save one’s fellow, the decision whether to do so belongs solely to the one harmed, not to anyone else. This is not about the severity of the prohibition but its nature.

It goes without saying that, according to this, harming a person’s rights is permitted if he grants permission. If Shimon agrees to give of his property or even of his body (as in an altruistic kidney donation), it is certainly permitted to take them to save another. This follows because the prohibition to harm Shimon is rooted in his rights, not in the severity of the act. If it were due to severity, Shimon could not waive it and permit it. Therefore, in the case of murder, for example, most decisors hold that one may not consent to sacrifice oneself for another. The reason is that murder is not set aside for pikuach nefesh because of its severity, not merely because it infringes the victim’s rights.[1]

The Law of the Pursuer (Rodef)

We have seen that one may not infringe one person’s rights without his consent in order to save another. It is well known that there is an exception to this principle in the law of the pursuer (rodef). If Shimon is pursuing Reuven to kill him, one may—and must—kill Shimon to save Reuven. At first glance, the law of rodef contradicts the earlier rule (“be killed rather than transgress” with respect to murder), for here we are preferring the blood of the pursued over the blood of the pursuer, harming this one to save that one. I will not elaborate here on the rationale for this distinction, only note that since the pursuer created the equation that sets his life against the life of the pursued, he is the one who must pay the price to resolve it. The pursuer’s culpability neutralizes the symmetry between the value of their lives, and therefore the pursuer’s life is subordinated to resolving the problem. For this reason we harm him to save the pursued. Again, not because his blood is intrinsically “less red,” but because, as the creator of the problem, the responsibility rests on him more than on anyone else.

It is important to note that actual culpability of the pursuer is not required; responsibility for the situation suffices. The Amoraim (see Sanhedrin 72b) debate a minor pursuer: whether one harms him to save the pursued. A minor lacks legal understanding and is not culpable for the pursuit, and of course he is not obligated in commandments and prohibitions; thus, ostensibly there is no justification to kill him—both because he is not at fault and because this does not “save him” from sin (Rashi’s view in Sanhedrin 73a is that killing the pursuer “saves” the pursuer himself from transgression). So why, nonetheless, is the halakhic ruling to kill even a minor pursuer? Because even if he is not at fault, he still constitutes a danger to others’ lives, and therefore responsibility for the situation lies with him, and, consequently, the law of rodef applies. Here there is a distinction between culpability (which a minor lacks) and responsibility (which exists even for a minor). After all, the danger that has arisen in the situation stems from him, even if not through his fault. The pursued is certainly no more at fault than he; there is no logic that because the pursuer is blameless, the pursued should pay the price. This is akin to the consideration of “your fortune caused it” (see Bava Batra 98a and parallels).

Back to Our Question

Let us return to the opening question. In light of what we have seen, in principle one is not permitted to infringe upon the mother against her will in order to save the fetus, even if the harm is not to her life (but rather surgery). True, here we are speaking of an operation rather than killing, but this resembles non-lethal harm to one in order to save another, which we saw is forbidden without his consent. Moreover, in this case the fetus is not necessarily in mortal danger—perhaps only at risk of disability or illness—which further diminishes the justification to harm the mother. Harming the mother could be permitted only if we view the mother as a pursuer vis-à-vis the fetus.

For the moment I will focus on two principled questions:

• Is such a situation indeed called “pursuit” (redifah)?
• Is the fetus considered a “life” (nefesh), such that one who endangers it is subject to the law of rodef?

These two questions relate to the Talmudic discussion in Sanhedrin 72b regarding a fetus that endangers its mother. Therefore we will begin with that sugya.

The Mishnah in Ohalot and the Sugya of Fetal Pursuit

The Mishnah in Ohalot 7:6 states:

A woman who is having a difficult labor—one cuts up the fetus in her womb and removes it limb by limb, for her life takes precedence over his life. Once its greater part has emerged, one may not touch it, for one does not set aside one life for another.

In the first clause we see that if the fetus endangers the mother’s life, it is killed in order to save her. The stated reason is that her life precedes his. It is not clear why: is it because she is a full person and he is not, and therefore her life is preferred? Or is it because he is deemed a pursuer against her (in which case, even if their life-values were equal, one harms the pursuer)? The second clause limits the first to when the fetus is wholly in the womb. If most of it (some versions: its head) has emerged, one does not kill it even if it endangers the mother, for one does not set aside one life for another. This appears to be precisely the “why is your blood redder” logic we saw above.

At first glance, the difference between the two clauses suggests that the first clause’s permissive ruling is not because the fetus is considered a pursuer; otherwise it would be permitted to kill it even after its head has emerged (one kills a pursuer who is a complete person). But the Gemara in Sanhedrin indeed discusses this, and its conclusion is not entirely clear. This arises in the context of the debate about a minor pursuer mentioned above.

At the start of that sugya, Rav Huna states that even a minor is subject to the law of rodef:

Rav Huna said: A minor who is pursuing [to kill] may be saved by taking his life, for he holds that a pursuer does not require prior warning—whether adult or minor.

Rav Chisda challenges him from the second clause of the Mishnah in Ohalot cited above:

Rav Chisda objected to Rav Huna: “If its head emerged, one may not touch it, for one does not set aside one life for another.” But why? It is a pursuer!

It appears he assumes such a case is pursuit. From here he infers that the second clause teaches that a minor is not a pursuer, and thus in his view this contradicts Rav Huna’s ruling. How would Rav Chisda explain the first clause, which permits killing the fetus, given his view that a minor is not a pursuer? We must say it is because the value of a fetus’s life is lower than that of the mother; thus, one prefers her to him. Here the “why is your blood redder” consideration does not apply, because the fetus’s blood is indeed “less red.”

But in the end, Rav Huna rejects Rav Chisda’s challenge, and thereby also his explanation of the Mishnah:

There it is different, for from Heaven they are pursuing her.

The Gemara says that, according to Rav Huna, this is not pursuit, since it is not the minor who chose to pursue the mother; rather, Heaven placed him in this situation. Note that this is stated even according to Rav Huna, who holds that a minor is indeed a pursuer. What is the difference between a fetus and a minor? A minor pursues by his own acts, though he lacks legal understanding; but the fetus is not there by any decision of his—it is by Heaven.

What does this mean for us? If this is not pursuit, then it is clear why, once the head or the majority has emerged, one does not kill him—for one does not kill Shimon to save Reuven. But then why, while he is still a fetus, does one kill him? Apparently because his life-value is not that of a complete person, and thus the “why is your blood redder” reasoning does not apply.

The difference between the initial thought (Rav Chisda) and the conclusion (Rav Huna) is the reason one kills the fetus. Both initially and in conclusion one kills him because his life-value is lower, not due to pursuit. But Rav Chisda thought this was a case of pursuit though a minor lacks the law of rodef, whereas Rav Huna held that, in principle, even a minor has the law of rodef—but this is not pursuit.

Note that the Gemara’s answer in Rav Huna’s view clears the minor not only of culpability but even of responsibility. It was obvious from the outset that he lacked culpability—for even if he had emerged, he lacks legal understanding (we are speaking of a fetus or a newborn). When the Gemara says this is not pursuit, it means that not only is he not culpable, he is not the one endangering the mother; the danger to her is from Heaven, through him. By contrast, in a case where a minor holds a weapon and is about to shoot the mother, according to Rav Huna one would certainly kill him by the law of rodef (this is Rav Huna’s ruling at the start of the sugya), for there is pursuit even if there is no culpability (he is a minor).[2]

In practice, Rambam rules thus (Laws of Murder 1:9; cited in Shulchan Aruch, Choshen Mishpat 425:2):

This is a negative commandment—not to have pity on the life of a pursuer. Therefore, the Sages ruled that a woman in difficult labor may have the fetus cut up in her womb—by drug or by hand—because it is like a pursuer after her to kill her; but once it has emerged its head, one may not touch it, for one does not set aside one life for another—and that is the nature of the world.

Several commentators have pointed out an apparent contradiction in his words. The first part seems to ground the permission to kill the fetus in the law of rodef. If so, one should be permitted to kill it even after the head has emerged, for the permission to kill a pursuer does not depend on his life-value but on his being a pursuer. Yet in the latter part, Rambam explains that one does not kill the infant after the head has emerged because one does not set aside one life for another—i.e., he does not view that case as pursuit.

The commentators suggest several approaches to Rambam, but the simple reading, in my view, follows R. Chaim of Brisk (and other Acharonim); I will formulate it in my own words. In the first clause, Rambam writes that the fetus in the mother’s womb is “like a pursuer” (not a pursuer), meaning: not fully a pursuer. This likely reflects the Gemara’s conclusion, “from Heaven they are pursuing her.” Thus, throughout, Rambam does not view the case as full pursuit. So why does he nonetheless tie the first clause to the law of rodef?

It seems that, in his view, this situation is a kind of attenuated pursuit—i.e., even the responsibility of the “pursuer” is incomplete (and certainly there is no culpability). Hence the fetus is only “like a pursuer.” The difference between a pursuer and “like a pursuer” is that “like a pursuer” permits killing the “quasi-pursuer” only when his life-value is not full—namely, while he is a fetus. That is the permission in the first clause. But once the head has emerged and he has full life-value, though he is still “like a pursuer,” there is no justification to kill him to save the mother, for the law of “like a pursuer” does not permit killing a complete person. This differs from the regular law of rodef, which permits killing even a complete person.

We thus learn that, according to Rambam, the permission in the first clause of Ohalot rests on a combination of two elements: there is a slight element of pursuit, and the “pursuer’s” life-value is not full. If one of these is missing (either there is no pursuit at all, not even attenuated, or we are dealing with a complete person), there is no permission to kill the “quasi-pursuer.” In both cases—i.e., where there is no pursuit or where there is “quasi-pursuit” but a complete person is involved—we revert to “saving oneself with another’s life,” which is of course forbidden (“be killed rather than transgress”).

Above, we asked two questions:

• Is such a situation truly pursuit?
• Is the fetus a nefesh, such that the law of rodef applies to one who endangers it?

Let us now see what the sugya implies regarding both.

The First Question: Is This a Case of Pursuit?

Regarding the first question, this depends on how we read the Gemara’s conclusion. Recall two possibilities: according to the straightforward reading, such a case is not pursuit, and the difference between the two clauses is the life-value of the “pursuer.” According to Rambam, it is attenuated pursuit (sufficient to justify killing a fetus).

Until now we assumed symmetry between the fetus’s status vis-à-vis the mother and her status vis-à-vis him. Note that the sugya discusses viewing the fetus as a pursuer of the mother, whereas our question is the reverse: can we view the mother as a pursuer of the fetus? By reasoning, these would seem identical, for in both situations “from Heaven they pursue them,” i.e., each is dragged into the situation against their will. If so, regarding the mother vis-à-vis the fetus, either there is no pursuit at all (as per the plain sugya) or there is attenuated pursuit (per Rambam).[3]

However, there is ample room to distinguish. The Gemara says the fetus is there against his will (by Heaven), and therefore he is not considered a pursuer of the mother (perhaps “like a pursuer,” per Rambam). But the mother chose to bring him into the world; she placed him there. Therefore, regarding the mother’s “pursuit” of the fetus, it would seem inappropriate to say “from Heaven they pursued him,” and thus the mother could indeed have the status of a pursuer vis-à-vis him. True, the risk to the fetus is not her initiative, but Heaven-sent; yet his very presence in her womb stems from her decision.

On reasoning, I would say the mother does have the status of a pursuer here, for she chose to bring him into the world, and therefore the responsibility for his welfare and life lies with her; if she can save him, she is obligated to. Perhaps not to kill her in order to save him, but to obligate her to undergo surgery seems very reasonable. However, the question of the fetus’s life-value now arises. Even if we decide the mother is a pursuer, she is “pursuing” something not entirely a person. Perhaps, for such pursuit, there is no permission to harm, because the pursued’s life-value is also not “full life.” One might distinguish between true pursuit (then one may harm her to save the fetus) and “quasi-pursuit” (which may not permit it). But it seems from the above reasoning that the mother is a full pursuer (the fetus, even without this reasoning, is only “like a pursuer”). Another implication: when the fetus is not in mortal danger but only at risk of disability—may one, or must one, harm the mother (without endangering her life) who is endangering him? If he is in mortal danger, it seems the mother is a pursuer, and the remaining question is whether we execute one who pursues a fetus.

The Second Question: Is the Fetus a Nefesh?

From Sanhedrin it would appear that a fetus’s life-value is not that of a full person. This is true both according to the plain sugya and according to Rambam. Likewise, one who kills a fetus is not liable to the death penalty like a murderer of a regular person. At the same time, it is clear that killing a fetus is not neutral. The Gemara in Niddah 44b explains that a Jew is liable to death only for killing a “nefesh,” and a fetus is not considered a nefesh. Nevertheless, as Tosafot (s.v. “leika”) in Sanhedrin 59a write, there is still a prohibition (and a non-Jew is even liable to death for it—see the Tannaitic dispute in Sanhedrin 57b; Rambam, Kings 9:7, for the practical ruling). Later authorities dispute the source: some write it is true murder (Igrot Moshe, Choshen Mishpat 2:69), though not punishable by death; others say it is a different, lesser prohibition (Tzitz Eliezer 9:51). Either way, a fetus’s life-value is not full.

Thus far we have discussed the prohibition and punishment for killing a fetus—i.e., the question of destroying a fetal life. Our question, however, concerns harming another or violating a prohibition for the sake of saving a fetus: is saving a fetus considered saving a life? One may ask this regarding desecrating Shabbat or other prohibitions to save it, or regarding the very obligation to save it. We address it here regarding whether the mother (whom we saw above is arguably defined as a pursuer against him) is obligated to undergo surgery to save him.

Saving a Fetus[4]

On this matter, the Gemara in Arakhin 7a–b states:

Rav Nachman said in the name of Shmuel: A woman who sat on the birthing stool and died on Shabbat—one brings a knife and tears open her abdomen and removes the fetus. Objection: Obviously—what else is he doing but cutting flesh? Rabbah said: It was necessary to teach that one brings the knife via the public domain [i.e., carrying on Shabbat]. And what does it teach us? That even for a doubt we desecrate Shabbat. But this is taught elsewhere: [If] a building collapsed on a person, and we do not know whether he is there or not, whether he is alive or dead, whether he is Canaanite or Israelite—we clear the debris. You might have said: there he had a presumption of life, but here, where he had no presumption of life from the outset, perhaps not. Therefore it teaches [that we do desecrate Shabbat].

We see that saving the fetus justifies (indeed obligates) desecrating Shabbat. The Gemara even wonders what the novelty is, and even in a case of doubt it takes for granted that Shabbat is desecrated. Thus, for purposes of desecrating Shabbat, a fetus is like a complete person—even for Torah-level violations and even in doubtful cases. Moreover, the Gemara assumes this is not a special novelty relative to an ordinary person. At the end, a distinction is suggested (regarding “presumption of life”), but rejected; and even the initial distinction concerns only that the fetus might not survive later, not the fact that he is a fetus. On the other hand, the case there is of a deceased mother; perhaps the fetus already counts as a living person, like one whose head or majority has emerged.

The Rishonim struggled to reconcile this with the rule above that a fetus’s life-value is less than that of a person. Several answers are recorded. The Shitah Mekubetzet there (note a) explains that the case is of a fetus whose head has already emerged; otherwise one does not desecrate Shabbat for him (and, presumably, one would not execute a pursuer against him). The Rosh in Yoma (8:13; and Tosafot Niddah 44b) writes that when the mother has died, the fetus is akin to one whose head has emerged (like one placed in a box), i.e., a living person. A second answer in Tosafot there and the Behag (cited by the Rosh) offer a third explanation: indeed, his life-value is less than that of a complete person—hence one kills him to save his mother—yet one still desecrates Shabbat to save him. The reasoning could be one of two: Tosafot write that there is value to his life, even if not full value (just as there is an intermediate state of “attenuated pursuit,” there is an intermediate life-value); therefore we desecrate Shabbat to save him (though his life-value is less than the mother’s, so we kill him to save her). The Ran (3b, s.v. “chutz”) writes that we apply the logic of “desecrate one Shabbat for him so that he will keep many Sabbaths,” for in the future he will observe many Sabbaths even if at present he is not fully alive.[5]

In practice, the Shulchan Aruch (Orach Chayim 330:5) rules not like the Shitah Mekubetzet, and holds that one must save the fetus even if the head has not yet emerged. Therefore, the halakhah appears to be that saving a fetus’s life justifies violating prohibitions, as with saving a complete person. Still, the fact that we desecrate Shabbat for a fetus does not necessarily mean his life-value also justifies infringing the mother’s rights. As we saw, at least according to the Ran, the obligation to desecrate Shabbat is justified by “desecrate one Shabbat so that he will keep many,” i.e., because he will in the future observe many Sabbaths, even if his present life-value is not sufficient to justify Shabbat desecration on its own. If so, one cannot infer from the obligation to desecrate Shabbat to save him that the law of rodef applies to one who seeks to kill him, yielding permission to harm the mother to save him. Harming the mother is not about committing an aveirah but about her rights; permission to infringe her rights cannot be grounded in the permission to desecrate Shabbat for his life (just as we saw one may not violate one person’s rights for another). True, if we view the mother as a pursuer, there is room to harm her—but that is to save the life of a complete person. To save a fetus, whose life-value is presumably lower, it is not clear that this permission exists even if she is deemed a pursuer.

On reasoning, it seems we do execute one who pursues a fetus, because, as we saw, killing a pursuer is not due to the severity of murder but because he threatens the rights of the pursued; therefore his life is subordinated to resolving the problem that he created. In other words, comparing life-values is irrelevant to the law of killing a pursuer; consequently, we kill even a high-value pursuer to save a lower-value pursued. Thus, if the mother is pursuing the fetus, even though her life is more valuable, we kill her. Admittedly, she is not pursuing intentionally—only bearing responsibility—and therefore this could be questioned. However, here we are speaking of harming the pursuer (operating on the mother), not killing her; this seems permissible.

Summary

Operating on the mother does not endanger her but does infringe her rights. Even such an infringement is possible only if the mother has the status of a pursuer; and perhaps it is also required that the pursued’s (the fetus’s) life-value be sufficient for the law of rodef to apply to one who endangers it (especially where the fetus is not clearly in mortal danger—perhaps only of illness or disability). Since we are not speaking of killing the mother but of infringing her rights, it seems that defining her as a pursuer (even without intent, but with responsibility—since she chose to bring him into the world, and thus into this difficult situation) suffices to obligate her to do so.

Bottom line, I would say that, halakhically, the mother is obligated to undergo surgery to save the fetus. In my understanding, this is how one should rule in practice. However, if she still refuses, it is hard to rule that she must be coerced to undergo surgery against her will. She may be a transgressor, but it is her right; only she can decide whether to give up her rights to save someone else. If she were a full pursuer, then even for a fetus there would be room to coerce her; but as we have seen, she is a pursuer by responsibility, not by a deliberate decision to harm the fetus. In any case, the burden of proof rests on whoever seeks to obligate her.

It seems we should distinguish between a case in which the mother claims her refusal is due to risk to herself (at least she believes there is a risk and fears it), in which case one cannot obligate her to endanger herself against her will (for she is not an intentional pursuer), and a case in which the refusal is due to inconvenience—where it is easier to obligate her. To understand this better, consider parents’ obligation to support their children. There it seems obvious that we compel them, even though this infringes their rights (their property). Note that in the case of parents of a child living in their home, it is not plausible to define them as pursuers, and yet they are deemed responsible for him because they brought him into the world. It may be inconvenient for them, but saving the child’s life and their responsibility for him, since they brought him into the world, justify infringing their rights. This does not mean one may kill them to save the child, since they are not pursuers; but they bear responsibility due to their decision to bring him into the world.

The question is whether undergoing surgery falls within that responsibility—i.e., whether such a demand is akin to infringing their rights to support the child (which is certainly imposed on them), or akin to harming them physically to save him (which perhaps is not imposed). We have seen that in our case it is reasonable to deem the mother a pursuer (for she herself endangers the fetus, unlike a case where she is harmed to save him), albeit without intent; therefore it may be permitted even to harm her. This, of course, further strengthens the side that one may obligate her to undergo surgery (even if not coerce her).

A Note on Method: First-Order Ruling

This column presents a first-order treatment of the issue. Note that I have hardly relied on sources—only on foundational principles from Talmudic sugyot and illustrative points from the Rishonim. In any case, I did not base the conclusion on precedents among Rishonim and Acharonim. My conclusion is grounded mainly in a conceptual and logical analysis of the situation—on sevara and common sense (I hope).

I must admit that, surprisingly, I have not found such a discussion in the halakhic literature (to be sure, I did not search extensively. After I replied to the questioner, I was told that Rav Elyashiv has a responsum on this topic; I am waiting to see it). Therefore I do not know whether a second-order discussion was possible here, even had I wished it. But even when there are no sources that address it, many second-order decisors would treat this as a doubt. I do not know how many would decide it on sevara.

[1] A very similar approach appears in Peninei Yekarim (cited also in Avnei Miluim §44) regarding the non-validity of kiddushin for a married woman. His claim is that, unlike other arayot (forbidden unions), for which kiddushin does not take effect because of the severity of the prohibition, in the case of a married woman the kiddushin fails also because she already “belongs” to someone else (she has no “hand” to accept kiddushin)—and, of course, also because of the severity of the prohibition. The consequence is regarding a “designated bondwoman” (shifchah charufah), who can be a married woman though the prohibition to cohabit with her is mild, if it exists at all—yet kiddushin does not take effect even there. See my article on the nature of the guilt-offering.

[2] The Jerusalem Talmud (Niddah 44a) explains that as long as the fetus is in the womb, he is certainly considered a pursuer of the mother, because he does not yet count as fully alive. But once the infant has emerged and has life, one can no longer determine who is pursuing whom—whether the mother endangers the infant or the infant endangers the mother—and therefore one may not kill either.

[3] It may in fact be a case of mutual pursuit. See Column 437 on this.

[4] See, for example, a survey here.

[5] True, in the conclusion of Yoma 85 this rationale is rejected—but only because it is insufficient to permit in cases of doubtful pikuach nefesh. In certain pikuach nefesh, this reasoning does stand in halakhah, and indeed the decisors cite it. Moreover, the Gemara in Shabbat 151b brings it regarding desecrating Shabbat for a child, similar to what the Ran writes here regarding a fetus.