It’s true that pregnenolone can become DHEA if much of it were exposed to the enzymes that make the conversion, as occurs when pregnenolone is produced in the adrenals, ovaries, or testes. In those instances, pregnenolone is produced in absolute hotspots for the enzymatic conversion.
The rest of the body has little to none of the needed enzymes, so the vast majority of supplemental pregnenolone has no hope of conversion.
Even the pregnenolone happening to reach for example the ovary as an organ wouldn’t be good enough: you would need a good percentage of the oral pregnenolone to get right inside the exact cells where the enzymes are. That’s just not plausible. The body has trillions of other cells which are going to get equal share, so to speak, so the vast majority of the pregnenolone has no hope of conversion.
To my knowledge increase in DHEA, estradiol, or testosterone levels has never been reported from administration of pregnenolone. This would be for the above reason.