Jewish Law on the Sabbath

The use of embryos from fetuses that have been aborted within forty days of conception is a delicate issue as well. The matter of using aborted fetuses in stem cell research is a complicated issue because it involves Jewish law pertaining to abortion. Jewish law states that a fetus can only be aborted if the mother's health is in danger. However, different rabbis have different interpretations on Jewish law regarding abortion before the fetus is forty days old. Rabbi Unterman who was the former Ashkenazi Chief Rabbi of Israel stated that the rights of a fetus are protected by the prohibition against murder which states that embryos should not be used prior to forty days because it constitutes murder, even if it is being used for research purposes. He quotes Nachmanides' law book called the Toras Ha'Adam which says that the Sabbath can be desecrated if it is to save a fetus' life because the fetus will be able to observe many Sabbath's in the future. Since the laws of the Sabbath can be overruled when a fetus is involved, Nachmanides can be interpreted to say that killing a fetus is considered murder, even before forty days.

Another argument made by Rabbi Yair Bachrach, author of the book Chavot Yair" is that destroying a fetus before forty days is considered to be wasting of a seed which is prohibited under Jewish law. The third reason why abortion should be prohibited even before forty days is brought up by Rabbi Yosef Trani who posits the idea that killing a fetus before forty days injures the mother. However, Rabbi Weinberg counters this notion by claiming that destroying a fetus prior to forty days is not considered to be harming the woman nor is it the killing of human life because there is no recognizable limb to destroy from the fetus. In addition, the Mishna states that a woman is not in a state of impurity called "tumat leida," if she has a miscarriage prior to forty days of having the fetus.