Why we should transfer frozen instead of fresh embryos The translational rationale

Frozen transfer allows embryos to implant and develop in a more physiologic environment. This review summarizes the research on the effect of the superovulated environment on implantation and embryo development.

Rachel Weinerman, M.D., Monica Mainigi, M.D.

Volume 102, Issue 1, Pages 10–18

Epidemiologic studies have shown an increased rate of adverse perinatal outcomes, including small for gestational age (SGA) births, in fresh in vitro fertilization (IVF) cycles compared with frozen embryo transfer cycles. This increase is not seen in the donor oocyte population, suggesting that it is the peri-implantation environment created after superovulation that is responsible for these changes. During a fresh IVF cycle, multiple corpora lutea secrete high levels of hormones and other factors that can affect the endometrium and the implanting embryo. In this review, we discuss both animal and human data demonstrating that superovulation has significant effects on the endometrium and embryo. Additionally, potential mechanisms for the adverse effects of gonadotropin stimulation on implantation and placental development are proposed. We think that these data, along with the growing body of epidemiologic evidence, support the proposal that frozen embryo transfer should be considered preferentially, particularly in high responders, as a means to potentially decrease at least some of the adverse perinatal outcomes associated with IVF.

  • Nice article and important topic.

    Thought you all might be interested in a recent review/book chapter from our group – we have been studying early pregnancy events/fertility for many years and in the last 10 years or so have clearly established the dramatic differences between embryos and especially endometrium and placenta from embryo transfer (embryos from ‘natural’ matings simply transferred ‘fresh’ from a donor to a recipient), IVF, and cloned (in our case, parthenotes) embryos and normal embryos (simply from a ‘natural’ mating) using primarily sheep as a model – these dramatic differences probably have to do with early differences, especially epigenetic, between embryos, with embryonic ‘quiescence,’ also known as diapause (or at least a diapause-like state) and differences between endometrium in these types of pregnancies. In addition, they help explain the relatively poor pregnancy and postnatal outcomes of these types of pregnancies.

    If anyone would like a copy of the review/book chapter (ref: 1. Reynolds LP, Grazul-Bilska AT, Palmieri C, Borowicz PP. 2014. Placental Vascular Defects in Compromised Pregnancies: Effects of Assisted Reproductive Technologies and Other Maternal Stressors. In: Advances in Fetal and Neonatal Physiology (Zhang L and
    Ducsay C, eds.), Advances in Experimental Medicine and Biology Series, Springer Science+Business Media, NY) or other related references (e.g., evidence for epigenetic differences in early embryos), please email me.

    Larry Reynolds
    University Distinguished Professor of Animal Sciences
    Director, Center for Nutrition and Pregnancy
    North Dakota State University
    Email: Larry.Reynolds@ndsu.edu

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