The Collaborative International Dictionary of English v.0.48:

Prenatal \Pre*na"tal\, a.
   Being or happening before birth.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prenatal
    adj 1: occurring or existing before birth; "the prenatal
           period"; "antenatal care" [syn: prenatal, antenatal,
           antepartum] [ant: perinatal, postnatal,
           postpartum]

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "prenatal":
   abecedarian, aboriginal, antenatal, autochthonous, beginning,
   budding, creative, elemental, elementary, embryonic, fetal,
   formative, foundational, fundamental, gestatory, in embryo,
   in its infancy, in the bud, inaugural, inceptive, inchoate,
   inchoative, incipient, incunabular, infant, infantile, initial,
   initiative, initiatory, introductory, inventive, nascent, natal,
   original, parturient, postnatal, pregnant, primal, primary, prime,
   primeval, primitive, primogenial, procreative, rudimental,
   rudimentary, ur