Mo. Rev. Stat. § 211.177: Grandparent's right to intervene in action, restrictions, termination.

1. A grandparent shall have a right to intervene in any proceeding initiated pursuant to the provisions of this chapter, in which the custody of a grandchild is in issue, unless the juvenile judge decides after considering a motion to intervene by the grandparent that such intervention is against the best interest of the child.

2. The right of a grandparent to intervene pursuant to the provisions of this section may terminate upon the adoption of the child except where the child is adopted by a stepparent, another grandparent or other blood relative.