The Collaborative International Dictionary of English v.0.48:

Nascency \Nas"cen*cy\ (n[a^]s"sen*s[y^]), n. [L. nascentia. See
   Nascent.]
   State of being nascent; birth; beginning; origin.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nascency
    n 1: the event of being born; "they celebrated the birth of
         their first child" [syn: birth, nativity, nascency,
         nascence] [ant: death, decease, expiry]

Moby Thesaurus II by Grady Ward, 1.0:

37 Moby Thesaurus words for "nascency":
   accouchement, babyhood, beginnings, birth, birth throes, birthing,
   blessed event, childbearing, childbed, childbirth, childhood,
   confinement, cradle, delivery, freshman year, genesis,
   giving birth, hatching, having a baby, inception, inchoation,
   incipience, incipiency, incunabula, infancy, labor, multiparity,
   nascence, nativity, origin, origination, parturition, pregnancy,
   the Nativity, the stork, travail, youth