Umbilical-cord blood, which contains a large number of stem cells, has proved useful in treating some blood-related diseases, such as leukaemia, anaemia and thalassaemia. It can be stored for up to 18 years, but can only be collected immediately after delivery. Tony Chung Kwok-hung, professor of obstetrics and gynaecology at Chinese University, said cord-blood collection was an easy process. However, he said that while collection for public use was encouraged, private storage was discouraged because only a small proportion of babies, estimated to be from one in 1,000 to one in 200,000, would eventually use the blood. Nevertheless, Simon Tsoi of Healthbaby, one of the city's few private cord-blood banks, said collecting the blood for private use was becoming more popular. Among about 20,000 mothers who gave birth in private hospitals last year, about 4,000 opted for collection, and the number was steadily increasing, he said. Hong Kong saw about 70,000 babies born last year, about 30 per cent of them in private hospitals. Cord-blood collection takes place in public hospitals, but only at Queen Elizabeth Hospital and Kwong Wah Hospital, and mothers must donate the blood to a public bank managed by the Red Cross. 'Cord-blood collection by commercial firms is not permitted in public hospitals,' a Hospital Authority spokesman said. A Red Cross spokesman said staff visited antenatal clinics at the two hospitals to provide information about cord-blood donation. Interested mothers needed to register, and then undergo an assessment for their suitability to donate. After collection in the delivery room, cord blood was taken for further processing, so that the stem cells could be concentrated, and was tested for infectious diseases. Cord blood was then stored in tanks of liquid nitrogen for future use, he said.