The Collaborative International Dictionary of English v.0.48:

Biparous \Bip"a*rous\, a. [L. bis twice + parere to bring
   forth.]
   Bringing forth two at a birth.
   [1913 Webster]

WordNet (r) 3.0 (2006):

biparous
    adj 1: producing two offspring at a time [syn: biparous,
           twinning]