The cause of death of a month-old baby whose mother stopped taking heroin when she was six months pregnant could not be established, a coroner found yesterday. Government pathologist Dr Wong Hon-man told the inquest he could not discover why Chan Lai-sheung's baby died on January 30 last year. Although her face was covered in milk vomited by her when her parents found her unconscious in bed, Dr Wong said she did not choke to death. But he said drug addicts' babies were more likely to die for unknown reasons. Coroner Richard Day recorded a verdict of death by natural causes. Ms Chan, 24, said she had decided at six months to continue her pregnancy and started methadone therapy for her habit. Mr Day said the case showed the folly of mothers-to-be taking drugs. Dr Tse Hei-yee, of Kwong Wah Hospital, said the baby was born one-third lighter than normal on December 25, 1995, and later experienced further growth retardation.