  We consider the nucleon-nucleon scattering problem by applying time-ordered
perturbation theory to the Lorentz invariant formulation of baryon chiral
perturbation theory. Using a symmetry preserving higher derivative form of the
effective Lagrangian, we exploit the freedom of the choice of the
renormalization condition and obtain an integral equation for the scattering
amplitude with an improved ultraviolet behavior. The resulting formulation is
used to quantify finite regulator artifacts in two-nucleon phase shifts as well
as in the chiral extrapolations of the S-wave scattering lengths and the
deuteron binding energy. This approach can be straightforwardly extended to
analyze few-nucleon systems and processes involving external electroweak
sources.
