The oblique parameters in multi-Higgs-doublet models
  We present general expressions for the oblique parameters S, T, U, V, W, and X in the SU(2)xU(1) electroweak model with an arbitrary number of scalar SU(2) doublets, with hypercharge 1/2, and an arbitrary number of scalar SU(2) singlets. 
W. Grimus, L. Lavoura, O.M. Ogreid, P. Osland