A woman whose son was taken from her care after she failed one in a series of drug tests is to have her case reviewed by Court of Appeal judges.
The woman - who is in her thirties - has questioned the validity of a test carried out on a strand of her hair.
She insists that she has stopped taking drugs and says more than 40 random tests were clear.
Now a senior judge has raised concerns about the case.
Lady Justice King - who sits in the Court of Appeal - says three appeal judges should reconsider the case.
She gave directions after analysing the woman's case at a preliminary appeal court hearing in London.
The judge said the woman had a history of drug taking, social workers were concerned about her ability to care for the youngster and wanted to be sure that she had stopped.
A local family court judge in London had overseen and monitored the case.
Lady Justice King said the woman had been co-operating with social services staff and the little boy, now nearly 18 months old, had been doing well in her care.
The woman had been randomly drug tested more than 40 times and all results were clear, said the judge.
But one test had been positive and a local judge had ruled that the little boy should go into local authority care and be placed for adoption.
The woman insisted that she had stopped taking drugs and has questioned the accuracy of the test.
She says a report by an independent expert backs her case.
Lady Justice King said she was "very concerned" about the case and said three appeal judges should examine evidence.
She said the little boy could not be identified.