According to McCoy, they're born pregnant.
McCoy says that they're "born pregnant", which is very inaccurate, since this is impossible. Tribbles probably would reproduce through a form of asexual reproduction called parthenogenesis. McCoy was simply being colloquial--a scientist addressing laypersons in that way, to put them at ease. What McCoy had to have meant was that the Tribble's parthenogenesistic reproduction process would have to commence very soon after, or coincident with, each individual's emergence thereto ProfessorTrek 09:37, September 8, 2011 (UTC)