IVF frozen embryos. Couple handing a thermos flask containing their frozen embryos to a technician during the in vitro fertilisation (IVF) process. The embryos are frozen in liquid nitrogen at -196 degrees Celsius. For IVF, fertility drugs are given to potential mothers to stimulate the production of several ova (eggs), rather than just one as normal. These are then fertilised in the laboratory using a fresh or frozen sample of the husband's sperm. If fertilisation is successful, the resulting embryos, contained in the flask, are implanted into the mother's uterus. 3-4 embryos are often introduced to increase the probability that one will implant. Photographed in France.