Halakhah for Chullin 147:25

From the laws of the commandment is, for example, that which they, may their memory be blessed, explained (Keritot 4b) that the prohibition of forbidden fat is only with the three beasts in Scripture - the ox, the sheep and the goat. And one is liable for the chelev of these three, whether they are fit (kosher), torn or carcasses. But the chelev of other types of animals - whether impure or pure - is like its meat. And so [too,] there is no prohibition of chelev in the fetus that is called the embryo that is in the innards of the three beasts mentioned. And therefore, they said (Chullin 74b) [about] one who slaughters an animal and found an embryo in it, [that] all of its chelev is permitted - and even if he found it alive. But if it finished its months and he found it alive - even though it did not hover over the ground and it does not require slaughter - its chelev is forbidden, and we are liable excision for it. And behold, its law is like [adult] beasts regarding its chelev. And hence we must remove all the fibers and all of the forbidden membranes from it. This is the opinion of Rambam, may his memory be blessed, (Mishneh Torah, Laws of Forbidden Foods 7:3) regarding an embryo that has finished its months - that there is a liability for excision with its chelev. But the majority of the commentators disagree with this and say that its chelev is permissible. And the words of the Gemara (Chullin 92b) decide like them. As behold we found Rabbi Meir and Rabbi Yehudah disagreeing about its chelev; and Rabbi Yehudah - whom we follow - is the one that permits it.