The Collaborative International Dictionary of English v.0.48:

Gravidity \Gra*vid"i*ty\, n. [L. graviditas.]
   The state of being gravidated; pregnancy. [R.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

gravidity
    n 1: technical terms for pregnancy [syn: gravidity,
         gravidness, gravidation]