Bismillahi Al-Rahmani Al-Rahim
What should be done with a miscarried fetus?
A miscarriage occurs before the fetus has reached four months, the fetus is washed and prayed over even if it did not cry or show other outward signs of life. It is desirable [mustahabb] to name the child. If it is not known whether the fetus was a boy or girl, a name fit for both is given.
If the miscarriage occurs before reaching four months, the tissue should be buried in a suitable place, however it is not washed nor prayed over.
Whenever possible, Muslims should try to bury any human tissue (even tonsils) in a suitable place. It should never be left for the hospital to incinerate it or worse.
And Allah knows best.
wa al-salamu `alaykum