Hadith: We asked the Messenger of Allah (may Allah's peace and blessings be upon him) about the fetus (of edible animals). He said: Eat it if you wish, for it is considered legally slaughtered with the slaughtering of its mother

عن أبي سعيد قال: سألْنا رسول الله صلى الله عليه وسلم عن الجَنِينِ فقال: «كُلُوهُ إنْ شِئْتُم، فإنَّ ذَكاتَه، ذَكاةُ أُمِّهِ».
[صحيح] - [رواه أبو داود والترمذي وابن ماجه وأحمد]

Abu Sa‘īd reported: We asked the Messenger of Allah (may Allah's peace and blessings be upon him) about the fetus (of edible animals). He said: "Eat it if you wish, for it is considered legally slaughtered with the slaughtering of its mother."
Sahih/Authentic. - [Ibn Maajah]

Explanation

The fetus of a slaughtered animal, if taken out dead, is lawful to eat. The slaughtering of the mother is enough to make it lawful to eat, for the fetus was part of the animal when it was slaughtered. Being so, the parts of the animals do not require independent slaughtering.