 From the insurers' point of view, medical underwriting is necessary to prevent people from purchasing health insurance coverage only when they are sick, pregnant or need medical care.Adverse selection is a system that attracts high-users and discourages low-users from participating.Proponents of underwriting believe that if given the ability to purchase coverage without regard for pre-existing medical conditions (no underwriting), people would wait to purchase health insurance until they got sick or needed medical care.