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BACKGROUND: Infertility affects one in seven couples; many of these need in vitro fertilisation (IVF). IVF involves external hormones to stimulate a woman's ovaries to produce eggs which are harvested surgically. Embryos, created in the laboratory by mixing eggs with sperm, are grown in culture for a few days before being replaced within the uterus (fresh embryo transfer). Spare embryos are usually frozen with a view to transfer at a later point in time - especially if the initial fresh transfer does not result in a pregnancy. Despite improvements in technology, IVF success rates remain low with an overall live birth rate of 25-30% per treatment. Additionally, there are concerns about health outcomes for mothers and babies conceived through IVF, particularly after fresh embryo transfer, including maternal ovarian hyperstimulation syndrome (OHSS) and preterm delivery. It is believed that high levels of hormones during ovarian stimulation could create a relatively hostile environment for embryo implantation whilst increasing the risk of OHSS. It has been suggested that freezing all embryos with the intention of thawing and replacing them within the uterus at a later stage (thawed frozen embryo transfer) instead of fresh embryo transfer, may lead to improved pregnancy rates and fewer complications. We aim to compare the clinical and cost effectiveness of fresh and thawed frozen embryo transfer, with the primary aim of identifying any difference in the chance of having a healthy baby. METHODS: E-Freeze is a pragmatic, multicentre two-arm parallel group randomised controlled trial where women aged ≥18 and 

Original publication




Journal article


Reprod Health

Publication Date





Assisted conception, Elective freezing, Fertility, Fresh embryo transfer, Frozen thawed embryo transfer, IVF, OHSS, Receptivity, Adolescent, Adult, Cost-Benefit Analysis, Cryopreservation, Embryo Implantation, Embryo Transfer, Embryo, Mammalian, Female, Fertilization in Vitro, Freezing, Humans, Infertility, Female, Live Birth, Ovarian Hyperstimulation Syndrome, Ovulation Induction, Pregnancy, Pregnancy Complications, Pregnancy Outcome, Pregnancy Rate, Young Adult