In vitro fertilisation. Preparation of donor sperm. Healthy motile sperm will swim upwards and can be separated off using a pipette. These sperm will be used to fertilise ova (eggs) in a petri dish. Fertility drugs cause women to superovulate, that is, produce more than one ovum. Ova are harvested by laparoscopy, or by ultrasound-guided needle aspiration through the vagina. Sperm is provided by the woman's partner or thawed from storage. In successful cases, embryos are trans- ferred to the woman via a catheter through the cervix. 3 or 4 embryos are often introduced, to increase the probability that one will implant. Photographed at St. Bartholomew's Hospital, London