Successful fertilization is only one half of the coin, implantation is the other half that is necessary that pregnancy can begin. As it is extremely difficult to observe normal human implantation not only for experimental, but for ethical reasons, too, the mouse is for several reasons the model of choice: implantation to occur at the blastocyst stage, only a narrow window for reception, decidualization of the stroma, invasion of the embryo into this stromal bed and a common hemochorial placentation.

In an excellent review in Molecular Endocrinology, Pawar, Hantak and Bagchi have summarized the actual knowledge about mouse implantation biology: crosstalk of estrogens and progesterons for proliferation and differentiation, estrogen and progesteron receptors at the start of signal cascades, paracrine factors as LIF, IHH, STATs, FGFs and EGF, the role of the stroma and the epithel. How the (experimental) lack of some of these proteins leads to infertility is convincingly described. It has not been a great surprise that they offer a explanation for endometriosis the disease where there is aberrant decidualisation in the peritoneum of women patients.

A must for gynaecologists!