On or after January 1, 1990, every group health maintenance agreement entered into or renewed that covers hospital, medical, or surgical expenses 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 maintenance organization in accord with standards set in rule by the board of health: PROVIDED, That such procedures shall be covered only if rendered directly by the health maintenance organization or upon referral by the health maintenance organization. Every group health maintenance organization shall communicate the availability of such coverage to all groups covered and to all groups with whom they are negotiating.