spontaneous abortion vs miscarriage

spontaneous abortion and miscarriage both are nouns.

Word	Noun	Adjective	Verb	Adverb
spontaneous abortion	Yes	No	No	No
miscarriage	Yes	No	No	No

As nouns, spontaneous abortion and miscarriage are synonyms defined as:

spontaneous abortion and miscarriage: a natural loss of the products of conception

Other synonyms of spontaneous abortion include stillbirth.

spontaneous abortion (noun)	miscarriage (noun)
a natural loss of the products of conception	a natural loss of the products of conception
	failure of a plan