Once a petitioner has received the adoptee into his home and a petition for adoption has been filed, the petitioner has temporary custody of the adoptee and is responsible for the care, maintenance, and support of the adoptee, including necessary medical or surgical treatment, except as provided in Sections 20-7-1900 through 20-7-1970. A postplacement investigation and report of this investigation pursuant to Section 20-7-1740 must be completed before the final hearing. Unless the adoptee is removed pursuant to Section 20-7-610, when adoptive parents have received the adoptee into their home for the purpose of adoption but no petition has been filed pursuant to Section 20-7-1730, the child-placing agency shall secure an order from the family court before removal of the child from the adoptive parents. At the hearing the burden of proof is on the child-placing agency to prove that continued placement with the adoptive family is not in the adoptee's best interest.