One of the most widespread debates in the contemporary Teshuvas of the last generation was regarding aborting a fetus that has been diagnosed with Tay-Sachs disease r”l. This heated disagreement mainly focused on two great Poskim, R. Moshe Feinstein and R. Eliezer Waldenberg, formerly known as the Tzitz Eliezer. The discussion began in 5735 when the Tzitz Eliezer was presented with a question from an individual asking about aborting a fetus—diagnosed with Tay-Sachs disease—after three months (first trimester). In a lengthy response, bringing down a multitude of different Rishonim and Acharonim to show that there is room for leniency brought down below, the Tzitz Eliezer concludes that it is permissible to abort the fetus up until seven months:
שו”ת ציץ אליעזר חי"ג סי' ק”ב:
At the beginning of 5737, R’ Moshe Feinstein was presented with a similar question. In contrast to the Tzitz Eliezer’s lenient proposal, R’ Moshe took a much stricter approach relying firmly on the words of the Rambam to come to his final ruling that abortion of any type, whether it be a healthy fetus or one with Tay-Sachs disease, unless it is almost certian that the mother will not survive, constitutes the איסור דאורייתא of רציחה:
שו”ת אגרות משה חושן משפט ב:סה:
Thus began an extensive back and forth between two of the greatest halachic giants of the last generation, leading to a topic still hotly debated today.The Halacha varies in context of levels of danger to the mother and stage of the pregnancy.
Therefore, it is imperative to consult a Rov in all cases, whether is seems to be a case where one should be maikel or machmir.