Separating Conjoined Twins by Rabbi Chaim Jachter


 “The ethics and morals involved in this decision are too complex for me. I believe they are too complex for you as well. Therefore I referred it to an old rabbi on the Lower East Side of New York. He is a great scholar, a saintly individual. He knows how to answer such questions. When he tells me, I too will know."

These words, referring to Rav Moshe Feinstein, were reportedly uttered by none other than Dr. C. Everett Koop in 1977, then chief of surgery at Children’s Hospital in Philadelphia, who was later to become the surgeon general of the United States during the Reagan administration. He made this statement to his staff when deliberating the ethics of a morally wrenching dilemma. Conjoined twin girls that shared one heart were born to a Kollel family in Lakewood, New Jersey. The heart had six chambers (a heart normally has four chambers) and without surgical intervention both twins would die within a year since the abnormal heart was unable to sustain both babies. The only chance of even one twin surviving was to sacrifice one twin in order for the other to survive, as the heart could sustain only one of the twins. The parents brought the babies for medical care to one of the world’s leading hospitals, Children’s Hospital in Philadelphia.

This situation posed a multifaceted moral and legal dilemma that needed to be resolved in a variety of venues. Dr. Koop sought and received legal immunity from the United States civil courts from being prosecuted for murder of a twin. Catholic doctors and nurses sought the guidance of their theologians to permit their participation in the surgery. The parents of the twins would give their consent to the surgery only if Rav Moshe Feinstein, regarded as the leading Halachic authority of the day, permitted sacrificing one twin to save the other. When Dr. Koop, a deeply religious man who studied Bible every day, was challenged by his staff as to the morality of killing one baby in order to save another, he replied that Rabbi Feinstein would provide the necessary moral guidance for this most difficult situation.

In the end, Rav Moshe Feinstein permitted the surgery after considerable deliberation and even fasting over this weighty matter. He did not, however, issue a written explanation for his ruling. Moreover, other great Poskim such as Rav Yaakov Kaminetzky (as reported by Professor Zev Lev in Tradition Summer 1997 page 80) disagreed with this ruling. A number of suggestions were offered to explain Rav Moshe’s decision but none were convincing. Finally, in the Fall 1996 issue of Tradition (pages 106-110), Rav J. David Bleich presented a convincing explanation of this ruling, based on another ruling of Rav Feinstein that appears in Teshuvot Igrot Moshe Yoreh Deah 2:60.

Sacrificing one Life to Save Another

Normally Halacha forbids sacrificing one life to save another. This principle is articulated by the Mishnah (Ohalot Chapter 7 Mishnah 6): A woman whose life is endangered during a difficult labor is permitted to have the pregnancy terminated to save her life. However, once the head of the baby has emerged, one cannot touch it as we are forbidden to kill one individual to save another (Ein Dochin Nefesh Mipnei Nefesh).

This principle is reinforced by the Talmud Yerushalmi (Terumot Chapter 8): A group of individuals on a journey and encounter evildoers who say to them, ‘Give us one member of your group or we shall kill the rest of you’ – let them all be killed and we must not release even one Jewish soul (Yemsaru Kulam V’al Yismasru Lahem Nefesh Achat B’Yisrael). Accordingly, not only can we not kill an individual in order to save the life of another individual but we cannot even kill an individual in order to save the lives of numerous people.

A Possible Exception to the Rule

The Yerushalmi poses a serious question on this principle from the episode that is related in Shmuel II Chapter 20. The Navi records the story of a “wise woman of the town of Avel Beit Ma’achah” who hands over the rebel Sheva ben Bichri to King’s David’s general Yoav ben Tzeruyah. She did so in order to spare the entire town from being destroyed by Yoav ben Tzeruyah for harboring Sheva ben Bichri. The Navi apparently condones the actions of this woman as it refers to her with the complimentary title “wise woman”. Accordingly, the Yerushalmi is puzzled why she is complimented when she sacrificed the life of one in order to save those of others.

The Yerushalmi cites two explanations for why the case of Sheva ben Bichri differs. Rav Yochanan claims that Sheva differs because he was designated for death by Yoav ben Tzeruyah, while Reish Lakish claims it is because according to Halacha, Sheva deserved the death penalty as punishment for rebellion, as one who rebels against the king may be put to death (Rambam Hilchot Melachim 3:8). The debate between Rav Yochanan and Reish Lakish remains unresolved as Rishonim debate as to whose opinion should be followed and the Rama (Yoreh De’ah chapter 147) cites both Rav Yochanan and Reish Lakish without deciding between the two opinions.

This debate, however, appears to be entirely irrelevant to the case of the twins in Children’s hospital. Neither child was “designated for death” nor was either baby guilty of a capital crime which would permit sacrificing one child to save another.


There is another circumstance where Halacha permits killing one individual to save another— a situation of Rodef (Rambam Hilchot Rotzeich Ushmirat Nefesh 1:9). One must kill an individual who is attempting to kill someone. Perhaps one of the twins can be construed as a Rodef since she is threatening the life of her twin. The Rambam (ibid.) is clear that even a baby may potentially classify as a Rodef even though it has no malicious intent.

Nonetheless, the status of each twin as a Rodef neutralizes the license to kill one to save another. Rav Akiva Eiger (Ketubot 33a) states that Halacha forbids a lethal intervention in a situation of mutual pursuers. For example, if one were witness to the famous duel between Aaron Burr and Alexander Hamilton one would be forbidden to kill one of them to save the life of the other. Similarly, since the two twins are both pursuing the others’ lives, the Halacha does not grant permission to kill one to save another. This is similar to the aforementioned Mishnah in Ohalot which forbids killing the baby in order to save the mother after the baby’s head has emerged from the birth canal.

Saving a Mother by Killing a Fetus

However, there is a situation where Halacha permits killing one of two mutual pursuers to save the other. The aforementioned Mishnah in Ohalot states “A woman whose life is endangered in hard labor is permitted to have the pregnancy terminated”. Rambam (ad. loc.) explains that the fetus is considered to be a Rodef to the life of the mother. The Rambam is astounding, since if the fetus is construed as a Rodef, why is it forbidden to kill the baby to save the mother even after it has emerged from her body? For a list of sources of the solutions offered to resolve this difficulty, see Rav Bleich’s Contemporary Halachic Problems 1:347-349.

Rav Moshe Feinstein (Teshuvot Igrot Moshe Y.D. 2:60) resolves the problem as follows. Rashi (Sanhedrin 72b s.v. Yatza Rosho) asserts that a fetus is considered as only potential life until it emerges from its mother’s body. Thus, explains Rav Feinstein, the mother and the fetus are mutual pursuers but “unequal pursuers”. The mother is pursuing only a potential life and the fetus is pursuing one who is fully alive. Accordingly, the fetus which pursues a full life is a qualitatively greater Rodef than the mother who pursues only a potential life. Therefore, Halacha sanctions killing the fetus to save the life of the mother.

Rav Bleich’s Explanation of Rav Moshe’s Ruling

Rav Bleich argues that the same reasoning applies to the case of the conjoined baby sisters. The sisters were unequal pursuers since the right side twin had no chance for survival of more than a year even if the left side twin were to be sacrificed. The left side twin, however, had a very reasonable chance of survival if the other twin were to be sacrificed. The right side twin’s life expectancy is regarded as only Chayei Sha’ah (temporary life; see Avodah Zarah 26a and a full explanation in Gray Matter 3:28-32) while the left side twin enjoyed the possibility of achieving a normal lifespan.

Thus, the baby twin girls could be construed as “unequal pursuers”, since the right side baby pursues only Chayei Sha’ah whereas the left side baby is pursuing one with a possibility to live a normal lifespan. It follows that the right side baby is a qualitatively greater Rodef than the left side twin and thus the right side may be sacrificed in order to save the left side baby. Finally, we have a cogent explanation for Rav Moshe’s ruling.

One the other hand, Rav Yaakov Kaminetzky might have rejected the analogy between the weaker and stronger twin on the one hand and a fetus and its mother on the other.  He may have reasoned that the difference between fetus and mother is far greater than the gap between the viable twin and the non-viable twin. The Halacha (at least in Rashi’s opinion) regards the fetus and mother to be classified in two distinct categories in which the fetus is not considered to be fully alive.  However, two human beings are not categorized differently due to different life expectancies (at least as far as permission to eliminate one in order to save the other).  In addition, he might have rejected Rav Moshe’s explanation of the Rambam which assumes that Rambam subscribes to Rashi’s belief that a fetus is only potential life. One could argue that there is no evidence that the Rambam shares Rashi’s view. I thank Rav Chaim Schertz of Harrisburg, Pennsylvania for helping me formulate these insights.


Rav Moshe’s ruling was implemented in practice by Dr. Koop and the right side twin was sacrificed in order to save the life of the left side twin. Sadly, the left side twin died a few weeks later not due to complications from the surgery but rather due to contracting hepatitis B from a blood transfusion. Although the loss of both of these precious children constitutes an enormous tragedy, a bit of a silver lining in this very dark cloud is the great Kiddush Hashem and honor of Torah generated by the enormous respect Dr. Koop accorded to Rav Moshe Feinstein’s ruling. May the study of Rav Moshe’s ruling serve to honor and elevate the Neshamot of these two dear girls.

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