labor pains vs birth pangs

labor pains and birth pangs both are nouns.

Word	Noun	Adjective	Verb	Adverb
labor pains	Yes	No	No	No
birth pangs	Yes	No	No	No

As nouns, labor pains and birth pangs are synonyms defined as:

labor pains and birth pangs: a regularly recurrent spasm of pain that is characteristic of childbirth

Other synonyms of labor pains include labour pains.

labor pains (noun)	birth pangs (noun)
a regularly recurrent spasm of pain that is characteristic of childbirth	a regularly recurrent spasm of pain that is characteristic of childbirth