Can the evil eye or envy cause the death and miscarriage of a developing fetus, after ruling out medical causes, or is this belief considered polytheism (shirk) with Allah? And how can one verify that what happened was due to the evil eye or envy, and what are its signs?

Killing may occur due to the evil eye, as stated in the Prophet's (peace be upon him) saying: "Most of what causes death in my Ummah, after Allah's decree and destiny, is the evil eye." This is a good (hasan) hadith. This does not go beyond being a divine decree from Allah Almighty, and it is not possible to definitively assert that death occurred due to an evil eye or envy.