ABSTRACT
The formation of a decidual layer from endometrial stromal cells is imperative to all mammals with invading embryos. The superfertility concept suggests that, rather than rejecting good quality embryos, the endometrium of women with Recurrent Pregnancy Loss allows the establishment of more clinical pregnancies, which are destined to fail, and would have otherwise been rejected in fertile women. The decidua is therefore much more than a passive bystander subject to the embryo's invasive potential; instead, the decidua has an active role in implantation by acting as a biosensor of developmentally competent embryos. A study that compared the response of decidualized endometrial cells to different quality embryos showed that those adequately developed trigger a surprisingly modest decidual response, whereas poor-quality embryos led to the inhibition of several factors important to early pregnancy. The decidual response is therefore stronger in response to abnormal embryos, which are likely to have more intense metabolic activity.
