THE doctor who performed the fertilisation that led to Hong Kong's first ''sperm injection'', or SUZI, baby will next month learn how to take the technique a stage further - and perhaps increase the success rate in the process. Dr Tony Chiu Tak-yu will go to Australia to learn ICSI - intra-cytoplasmic sperm injection - in which the sperm is injected directly into the mother's egg. In SUZI (sub-zonal insemination) the sperm is fired through the egg's outer protective capsule but left outside the cell membrane to do the rest of the job itself. The technique can be used in the 10 per cent of cases when standard in vitro fertilisation - the mixing of eggs and sperm together outside the body - fails. The problem can be weak or too few sperm, or an egg with a particularly hard outer shell, says Dr Christopher Haines of the assisted human reproduction unit at the Prince of Wales Hospital. The best ICSI success rate - 30 per cent from egg to pregnancy - has been achieved in Brussels, according to Dr Haines. The Prince of Wales unit treats between 200 and 250 couples a year. SUZI typically has a five to 15 per cent success rate, according to Dr Simon Fishel of the obstetrics and gynaecology department of the University of Nottingham, where Dr Chiu was first trained. Of 24 couples who had received SUZI treatment at the Prince of Wales, five had been implanted with embryos. Two pregnancies resulted and one miscarried. The anonymous parents of Hong Kong's first SUZI baby had been public patients.