premie vs premature baby

premie and premature baby both are nouns.

Word	Noun	Adjective	Verb	Adverb
premie	Yes	No	No	No
premature baby	Yes	No	No	No

As nouns, premie and premature baby are synonyms defined as:

premie and premature baby: an infant that is born prior to 37 weeks of gestation

Other synonyms of premie include preemie, premature infant, preterm baby, preterm infant.

premie (noun)	premature baby (noun)
an infant that is born prior to 37 weeks of gestation	an infant that is born prior to 37 weeks of gestation