Marilen Benner

CHAPTER 1 12 of high-quality embryos is seen in recurrent implantation failure (RIF), mostly perceived as infertility. On the other hand, failure to exclude erroneous embryos in the peri-implantation period likely leads to miscarriage later on during gestation. Thus, the decidua holds a key role. Even after correct implantation is achieved, this highly specialized tissue continues to determine the faith of pregnancy in a second checkpoint: through enabling formation of the placenta. 5 6 7 8 91011121314151617181920 500 250 Number of miscarriages (in 90.000 pregnancies) Implantation failure Early pregnancy loss Miscarriage* Live birth (30%) 30% 30% 10% Pre-clinical (Prior to missed menses) Clinical (Pregnancy recognized) Where have all the conceptions gone? 1st trimester 2nd trimester Gestation Figure 1. Only a third of all conceptions lead to the birth of a living baby. The majority of conceptions is lost prior to recognition of the pregnancy. A third of all conceptions are carried to live birth. The majority of recognized miscarriages occurs in the first trimester. *After 28 weeks of gestation, pregnancy loss is termed “stillbirth”. Adapted from Macklon et al. 2002, Nilsson et al. 2014.