 However, in most cases, an insurer's ability to "re-underwrite" an existing guaranteed renewable policy is limited by contract provisions and the Affordable Care Act (previously by state law).Even so, premiums fluctuated significantly for existing policies if the average health of the policyholders with a particular product deteriorated, as often happened when rising premiums drove healthier individuals (who were able to buy other policies on more favorable terms) out of the product, leaving those who were relatively less healthy.One factor that drove that is the increase in costs, as individuals who initially pass underwriting develop health problems.