Wash. Rev. Code § 48.44.344
On or after January 1, 1990, every group health care services contract entered into or renewed that covers hospital, medical, or surgical expenses on a group basis, and which provides benefits for pregnancy, childbirth, or related medical conditions to enrollees of such groups, shall offer benefits for prenatal diagnosis of congenital disorders of the fetus by means of screening and diagnostic procedures during pregnancy to such enrollees when those services are determined to be medically necessary by the health care service contractor in accord with standards set in rule by the board of health. Every group health care services contractor shall communicate the availability of such coverage to all group health care service contract holders and to all groups with whom they are negotiating.
RCW 48.44.344
Prenatal testing-Limitation on changes to coverage: RCW 48.42.090.