Mo. Rev. Stat. § 376.818: Eligibility for Medicaid may not be considered by insurers.

No individual or group insurance policy providing coverage on an expense-incurred basis, no individual or group service or indemnity contract issued by a not-for-profit health services corporation, no health maintenance organization nor any self-insured group health benefit plan of any type or description shall be offered, issued or renewed in this state by any insurer on or after July 1, 1994, if any insurer, including a group health plan, as defined in section 607(1) of the federal Employee Retirement Income Security Act of 1974, takes into account that an individual is eligible for or is provided medical assistance under Medicaid (Title XIX) when enrolling an individual or in making payment for benefits to the individual or on the individual's behalf.