Which of the following highlights of the ACA prevents insurers from denying coverage?

The highlight of the Affordable Care Act (ACA) that prevents insurers from denying coverage is the requirement for coverage of pre-existing conditions. This provision fundamentally transformed the healthcare insurance landscape, ensuring that individuals with chronic illnesses or previous health issues cannot be denied coverage or charged higher premiums based on their health status.

Before the ACA, insurers often refused to cover individuals with pre-existing conditions, making it difficult for many to secure necessary healthcare. By mandating that insurance companies provide coverage regardless of an individual's health history, the ACA aimed to expand access to healthcare and reduce health disparities, promoting a more inclusive system.

The other options, while relevant to broader healthcare reforms, do not specifically address the issue of denial of coverage by insurers. Increased insurance premiums relate to cost considerations, mandatory maternity leave pertains to employment benefits rather than direct insurance coverage, and the implementation of insurance copays involves cost-sharing rather than accessibility to coverage itself. Thus, the requirement for coverage of pre-existing conditions stands out as the key mechanism for preventing denial of insurance coverage.