preterm infant vs premature infant

preterm infant and premature infant both are nouns.

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

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

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

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

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