Norfolk County Council has apologised to the woman, who lives in Norfolk, and her parents, who fought a two-year battle to clear their daughter's name.
The woman's unborn child was wrongly placed on a child protection register.
Social workers were criticised for treating rumours about the woman, who had a mental health disorder, as fact.
'Insufficient evidence'
The council said the inquiry into the case also found that some evidence had been destroyed.
It called a social worker's report "inaccurate, unrepresentative and unbalanced".
The woman's unborn baby was wrongly placed on a child protection register by Norfolk County Council, the independent inquiry decided.
The inquiry panel found there was "insufficient evidence" to justify doing so.
Lisa Christensen, director of children's services for the county council, said: "A panel wholly independent of the council examined the complaint and how it was dealt with, and made a number of recommendations."
She added: "We apologise wholeheartedly and unreservedly for the errors made and the consequent distress to the family, and we are ensuring that the necessary lessons are learned."
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