We consider the final step of a phase transition process in saturated solutions when particles coalescence (Ostwald ripening) and coagulation are possible to happen concurrently. A parametric solution to unsteady Smoluchowski integro-differential equation with constant coagulation kernel is found taking the diffusion mechanism of particles in the space of their volumes into account. The particle-size distribution is given by an exponentially decreasing bell-shaped function describing the experimental data at long times. The theory is extended to describe the cases of different coagulation mechanisms, hydrodynamic flows and external forces.