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

Bulletins and Announcements:

• 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:

  “denial of coverage for medically necessary treatment based on an individual’s gender identity of gender dysphoria by any Carrier is sex discrimination that is prohibited under Massachusetts law”.