A rare mix-up involving embryo biopsy specimens at Heal Fertility, a privately-run reproduction clinic in Hong Kong linked to former financial secretary Antony Leung Kam-chung, has prompted investigations by health authorities and policeThe South China Morning Post looks into fertility treatments in the city and how they are regulated.1. What is in vitro fertilisation?In vitro fertilisation (IVF) is a fertility treatment offered to couples struggling to conceive naturally.A woman receiving IVF will need to go through four steps. First, her ovaries are stimulated to help grow multiple eggs at the same time. The eggs are then collected. Sperm collected from the husband is mixed with or injected into the eggs. Successfully developed embryos are then transferred to the woman’s body.IVF programmes in the city were first initiated by the Chinese University of Hong Kong (CUHK) in 1984, while the first successful IVF pregnancy and delivery was carried out by the private Hong Kong Sanatorium and Hospital in 1986.2. How did the mix-up happen?Authorities revealed on Tuesday that the clinic had arranged for two couples to receive pre-implantation genetic testing (PGT) in May, before embryos were transferred into their bodies. Biopsy specimens were retrieved from the embryos, and sent to a diagnosis centre under CUHK for chromosomal testing to look for any genetic abnormalities.