Patrick O'Brien, a consultant obstetrician at UniversityCollegeLondonHospitals, said such a case would be seen about "once a year" - but there there were no accurate figures.
The study is taking place in collaboration with Professor Alan Thompson at the National Hospital for Neurology and Neurosurgery (part of UniversityCollegeLondonHospitals NHS Foundation Trust) and Institute of Neurology, UniversityCollegeLondon.
UniversityCollegeLondon academics interviewed paediatricians at 177 hospitals in England and Wales and found a lack of knowledge about the warning signs of children being underweight.
In the last few months I've seen new hospitals like UniversityCollege in London, the new Queen Elizabeth Hospital planned in Birmingham or Whiston Hospital in Knowsley, where I laid the foundation stone.