This article investigates the fundamental limitations on quantum coherence arising from intrinsic quantum properties and spacetime geometry, distinct from environmental decoherence. By applying theHeisenberg Uncertainty Principle (HUP) and analyzing wavepacket dynamics, we derive characteristic velocity scales ( v_spread, v_crit) and a critical frequency ( ω_c) that mark transitions in quantum behavior. We further explore how spacetime curvature introduces a geometric length scale ( L_curv), potentially influencing coherence in extreme environments. This unified framework provides quantitative thresholds relevant for understanding coherence persistence in systems like ultracold atoms, neutron interferometry, nanomechanical resonators, and explores the interplay between quantummechanics and geometry.