It depends on where the policy is underwritten. My guess is if you purchased the policy on the DC exchange, it's underwritten in DC and therefore DC laws and regulations would apply to the policy. It looks like plans underwritten in DC are required to cover what they consider "habilitative services" for children born with various conditions. You can read the code here:
https://code.dccouncil.us/us/dc/council/code/titles/31/chapters/32A