Surplus embryos are frozen embryos which remain after people have decided that their family is complete – the embryos are surplus to their own needs. They are a chance outcome of fertility treatment. People undergoing fertility treatment are typically focussed on getting the best chance of having a baby. Usually, the number of viable embryos at the completion of a treatment cycle is limited by natural attrition along the IVF process, from egg collection, fertilisation, and embryo development.