משנה אויף דברים 3:16

If the daughter of an Israelite was married to a priest who died and left her pregnant, her slaves may not eat terumah because of the share of the fetus, since a fetus prevents [its mother] from eating [terumah] but does not cause her to be able to eat [terumah], the words of Rabbi Yose. They said to him: since you have testified to us concerning the daughter of an Israelite who was married to a priest, even concerning the daughter of a priest who was married to a priest, and he died and left her pregnant her slaves may not eat terumah because of the share of the fetus!