Fresh versus frozen embryo transfer: Backing clinical decisions with scientific and clinical evidence

Abstract

Background: Improvements in vitrification now make frozen embryo transfers (FETs) a viable alternative to fresh embryo transfer, with reports fromobservational studies and randomized controlled trials suggesting that: (i) the endometrium in stimulated cycles is not optimally prepared for implantation; (ii) pregnancy rates are increased following FET and (iii) perinatal outcomes are less affected after FET. methods: This review integrates and discusses the available clinical and scientific evidence supporting embryo transfer in a natural cycle. results: Laboratory-based studies demonstrate morphological and molecular changes to the endometrium and reduced responsiveness of the endometriumtohC..