A mechanical reduction gear of a turbine engine, in particular for an aircraft, includes a sun gear having external toothing, a ring gear which extends around the sun gear and has internal toothing, planet gears which are in mesh with the sun gear and the ring gear and which have toothings of different diameters, a planet carrier which supports bearings for guiding the planet gears in rotation, and a lubrication circuit of the reduction gear. The planet carrier has a hydrodynamic abutment on which the sun gear is configured to bear axially.