Dr Toni Wolff, a paediatrician at Nottingham City Hospital, helped diagnose Mia and said research was desperately needed.

BBC: Six-year-old Nottingham girl Mia Blackwell cannot smile

Richard Hubbard, professor of respiratory epidemiology at Nottingham City Hospital and a spokesman for the British Lung Foundation, said breath analysis was already being used to diagnose children with asthma.

BBC: Lung infection identified using 'breath-print'

Mr Liu, a consultant obstetrician and gynaecologist at City Hospital, Nottingham, urged caution.

BBC: NEWS | Health | Drug may help avoid prematurity