Md. Code Ann., Fam. 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:
Added by Acts 2004, c. 502, § 2, eff. Oct. 1, 2004.