Which statement is true regarding the coverage of preventive services?

The statement that preventive services must be performed in-network is true because insurance plans typically design their coverage policies to encourage members to utilize in-network healthcare providers for preventive services. This approach helps to keep healthcare costs down for both the insurer and the insured. In-network providers have agreed to set prices with the insurance company, which usually results in lower out-of-pocket costs for the patient.

Preventive services, such as vaccinations, annual check-ups, and screenings, are generally covered at no additional cost to the insured when they are performed by in-network providers. This policy aims to promote regular health check-ups and early detection of potential health issues, as it aligns with the broader goals of preventive care to improve overall public health and reduce healthcare costs over time.

In contrast, the other options suggest limitations or restrictions on the coverage of preventive services that do not align with how they are generally structured in most health insurance plans. Preventive services are not contingent upon referrals, nor are they restricted to specific months, which further supports the validity of the correct answer.