live birth vs nascency

live birth and nascency both are nouns.

Word	Noun	Adjective	Verb	Adverb
live birth	Yes	No	No	No
nascency	Yes	No	No	No

As nouns, nascency is a hypernym of live birth; that is, nascency is a word with a broader meaning than live birth:

live birth: the birth of a living fetus (regardless of the length of gestation)
nascency: the event of being born

Other hypernyms of live birth include birth, nascence, nativity.

live birth (noun)	nascency (noun)
the birth of a living fetus (regardless of the length of gestation)	the event of being born