Geometries for five dimers linked by O-(HO)-O-... hydrogen bonds (HBs) are optimized in MP2/6-311++G-(d,p) ab initio calculations for several short intermonomer distances R. Several molecular descriptors obtained from the topology of the electron density rho(r) and electron localization function eta(r) gradient fields are obtained at these geometries. Changes with R of topological descriptors of rho(r) and eta(r) show that they continue to exhibit features characteristics of strong hydrogen bonding even at distances shorter than equilibrium R-eq. Only at very short R where unstable dissociative structures appear do they exhibit features clearly indicative of weak interaction. Hence, topological indices of rho(r) and eta(r) fail to identify unambiguously R-eq among other distances within a given HB system.