premature labour vs premature labor

premature labour and premature labor both are nouns.

Word	Noun	Adjective	Verb	Adverb
premature labour	Yes	No	No	No
premature labor	Yes	No	No	No

As nouns, premature labour and premature labor are synonyms defined as:

premature labour and premature labor: labor beginning prior to the 37th week of gestation

premature labour (noun)	premature labor (noun)
labor beginning prior to the 37th week of gestation	labor beginning prior to the 37th week of gestation