FGI is also known as the Facilities Guidelines Institute. They publish guidelines specifically for the design and construction of healthcare facilities, including hospitals.
Since FGI publishes guidelines, each state may choose to follow them differently, or even not at all, opting instead to create their own standards to follow.
Still, many states choose to adopt the Guidelines as law. Those states are able to choose what editions of the Guidelines they want, with the most recent edition being published in 2018.
43 states currently adopt the FGI Guidelines.