premature infant vs premie

premature infant and premie both are nouns.

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

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

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

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

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