Review of factors essential for blastocyst implantation for their modulating effects on the maternal immune system.

Pituitary and ovarian hormones prepare the endometrium for successful blastocyst implantation and support its process directly or indirectly through the action of growth factors, cytokines and other molecules. Many of the blastocyst implantation essential factors (BIEFs) are modulators of the maternal immune system. Since little is known as to the action of these molecules on the uterine lymphocytes, its clarification is imperative to the understanding of the process of blastocyst implantation.