Md. Code, Family Law § 9.5–203

Except as otherwise provided in § 9.5-204 of this subtitle, a court of this State may not modify a child custody determination made by a court of another state unless a court of this State has jurisdiction to make an initial determination under § 9.5-201(a)(1) or (2) of this subtitle and:

(1) the court of the other state determines it no longer has exclusive, continuing jurisdiction under § 9.5-202 of this subtitle or that a court of this State would be a more convenient forum under § 9.5-207 of this subtitle; or

(2) a court of this State or a court of the other state determines that the child, the child’s parents, and any person acting as a parent do not presently reside in the other state.