Massachusetts has explicit insurance guidance on transgender-related health care.

Bulletins and Announcements:

• Bulletin: Bulletin 2021-11, Prohibited Discrimination on the Basis of Gender Identity or Gender Dysphoria Including Medically Necessary Gender Affirming Care and Related Services
  Issued by: Commissioner Anderson
  Issued on: Sept. 9, 2021
  Summary:

  “Carriers may not categorically exclude services used in the treatment of gender dysphoria when those services are medically necessary or when the same services are covered for the treatment of other conditions. Carriers should consult the most up-to-date medical standards set forth by nationally recognized medical experts in the transgender health field, including but not limited to those issued by the World Professional Association for Transgender Health (WPATH). Carriers may not single out a treatment or procedure for exclusion of coverage because of its association with transgender people or with gender dysphoria. Additionally, where a treatment is considered medically necessary for a patient, other procedures required in preparation for, as a component of, as a follow-up to, or as a revision of the treatment should also be considered medically necessary and should not be denied based on an individual’s gender identity or because the services are being used in the treatment of gender dysphoria. Carriers may not impose requirements for coverage of a service when used to treat or ameliorate symptoms of gender dysphoria than when used to treat other conditions.”

• Bulletin: Bulletin 2014-03, Guidance Regarding Prohibited Discrimination on the Basis of Gender Identity or Gender Dysphoria Including Medically Necessary Transgender Surgery and Related Health Care Services (2014)
  Issued by: Massachusetts Office of Consumer Affairs and Business Regulation, Division of Insurance
  Issued on: June 20, 2014
  Summary:

  “...[D]enying medically necessary treatment based on an individual’s gender identity of gender dysphoria is sex discrimination under Massachusetts law."