Foreigner man adopting Thai step-child - Mother's rights?

Hello all,

just looking for some clarification and information.

I have been told that in the case of Thai adoption, the biological parent loses their rights regarding their child.

This is in the context of a foreign man going through a formal thai adoption of their (Thai) step-daughter. Would the natural Thai mother retain all of her rights?

In the case that I have heard correctly, could someone point me to some official documentation that specifies this? Further, in the case that the marriage goes south, and the foreign partner is vindictive, what protection is there for the child? (In terms of the natural mother keeping their child)?

Thank you