Tay-Sachs is an incurable genetic disorder caused by the lack of the vital enzyme hexosaminidase-A (Hex-A). Those born with the disease begin to lag in their physical and intellectual development starting at about six months old. This is followed by blindness and paralysis, then death, generally by the age of four. Nowadays, testing can determine with certainty whether a fetus has Tay-Sachs. If it does, the question arises: is it permissible to abort?
According to those who adopt the restrictive approach, the prohibition of abortion is an offshoot of the prohibition of murder, and just as it is forbidden to kill a sick person, so too it is forbidden to kill a sick fetus. Thus, it is forbidden to abort a Tay-Sachs fetus (R. Moshe Feinstein in Igrot Moshe, ḤM 2:69). R. Auerbach and R. Elyashiv rule this way as well; however, if the mother’s knowledge that she will give birth to such a sick baby leads to such a terrible emotional state that there is concern for her mental health, even these poskim permitted abortion, because mental illness can be life-threatening, and the mother’s life takes precedence over that of the fetus (Nishmat Avraham, ḤM 425, n. 18). (R. Feinstein does not permit an abortion even then; according to him, abortion is permitted only when it is almost certain that the mother will die.)
In contrast, according to those who adopt the permissive approach, abortion is allowed even when there is no concern that the mother of the Tay-Sachs fetus will become mentally ill, for they do not view abortion as murder, but as ḥavala or hashḥata. If so, it is preferable to prevent the fetus from the terrible suffering that would be its lot; it is better for this fetus not to be born at all. It is also best to spare the mother the terrible anguish of seeing her child suffer, without being able to do anything to help (Amud Ha-yemini §32). Obviously, it is best to perform the abortion as early as possible. However, be-di’avad, R. Waldenberg permits performing this abortion until the seventh month (Tzitz Eliezer 13:102).
As we saw (section 3 above), in practice one may rely upon those who rule permissively in cases of great necessity.
When possible, it is preferable not to perform an abortion directly using surgery, but rather to do it indirectly by having the woman take a labor-inducing drug. Some poskim maintain that even those who maintain that abortion is a Torah prohibition would agree that an indirect abortion such as this is prohibited only rabbinically, and thus can be permitted when circumstances are pressing. This is the position of R. Yehuda Ayash in Responsa Beit Yehuda, EH 14, and R. Ḥayim Palachi in Responsa Ḥayim Ve-shalom, EH 40. Chemical curettage, which involves administering a lethal drug to kill the fetus in the gestational sac, is also preferable to direct surgical termination, because using a drug might be considered indirect abortion.