Endometrial receptivity: miRNAs signing in?

mbryo implantation is complex and dependent on various factors in order to be successful. These factors include female age, embryo quality and chromosome constitution, endometrial receptivity, the female immune system status, and the embryo transfer method. Repeated implantation failure (RIF) generally is defined as the failure of a couple to conceive after the transfer of ≥10 good-quality embryos or after three in vitro fertilization (IVF) cycles. The interaction between the blastocyst and endometrium is critical for a pregnancy to be established and maintained. This interaction occurs during what is known as the window of implantation (WOI), which is a narrow time frame of maximal endometrial receptivity (reviewed by Craciunas et al. [1]). In recent years, several approaches have been developed and used clinically as biomarkers of endometrial receptivity and the WOI. Examples include endometrial thickness and pattern, Doppler indices, and the identification of patterns of endometrial gene expression considered to be representative of its receptive status (1). Another such group of potentially clinically useful biomarkers are microRNAs (miRNAs) which have been shown to be involved in the regulation of the genes responsible for the WOI timing (reviewed by Chen et al. [2]).