No, they will not be effective for stopping bleeding.
Here is a related video that covers an adjacent topic:
Tampons for Gun Shot Wounds - On Her Own
They're looking at tampons rather than pads, and specifically in the context of a gunshot wound, but the principles are the same. Feminine hygiene products (tampons, pads, cups, etc.) are not designed to stop bleeding. They're designed to relatively comfortably absorb a fairly small amount of blood. They're not hoping to stop any bleeding (in this context, "better out than in"), just to prevent that blood and uterine lining from embarrassing the user.
Medical gauze is designed to be more absorbent than pads. It's also designed to be inserted into the wound to aid in clotting at the site of bleeding.
For stopping bleeding, a sanitary pad may be better than nothing, but it is not better than gauze.