The role of frozen–thawed embryo replacement cycles in assisted conception

Abstract

Key content Recent years have seen a dramatic rise in the number of frozen-thawed embryo replacement (FER) cycles. Improved embryo cryopreservation techniques have resulted in outcomes for FER that are similar to fresh embryo transfer. FER maximises the cumulative live-birth rate of a fresh in vitro fertilisation (IVF) cycle by using excess embryos and encourages a policy of single embryo transfer; this has contributed to a fall in the multiple pregnancy rate associated with IVF. Freezing all suitable embryos in a fresh cycle reduces the risk of ovarian hyperstimulation syndrome. The endometrium is prepared for FER by a natural or medicated protocol; the optimum method is unknown. Learning objectives To appreciate the importance of FER in IVF practice. To understand the current debate surrounding fresh versus frozen IVF. To understand the indications for, and methods of, embryo cryopreservation. To understand the commonly used methods of endometrial preparation for FER. To be able to date an FER pregnancy. Ethical issues Funding from the National Health Service (NHS) for embryo storage and FER varies widely across the UK; where funding is limited, this can result in viable embryos being discarded. When an embryo is created by a couple, the consent of both partners is required before transferring the embryo.