Early detection of embryonic post implantation failures by ultrasound biomicroscopy and the role of the maternal immune system

Spontaneous embryonic resorption is considered a major problem in human medicine, agricultural animal production and in conservation breeding programs. Its causes and the underlying mechanisms have been investigated in the well characterized mouse model. However, most studies rely on post mortem examinations and have severe limitations because of the rapid disintegration of embryonic structures. The aim of this thesis was to establish a reliable method to identify embryo resorptions in alive animals at the earliest possible stage by ultra-high frequency ultrasound which will allow us to better understand and further investigate its underlying mechanisms because it avoids the onset of a general immune response. In my study, I provide a temporal time course of embryo resorption. Four stages of the resorption process were described in detail: first the conceptus exhibited growth retardation, second, bradycardia and pericardial edema were observed, third, further development ceased and the embryo died, and finally the embryo remnants were resorbed by maternal immune cells. During early gestation (day 7 and 8 of gestation), the first stage was characterized by a small embryonic cavity. The embryo and its membranes were ill defined or did not develop at all. The echodensity of the embryonic fluid increased and within one to two days, the embryo and its cavity disappeared and were transformed into echodense tissue surrounded by fluid filled caverns. During later gestational stages (day 9 to 11), the resorption prone conceptus was one day behind normal siblings in its development. Growth retarded conceptuses exhibited bradycardia and ultimately cessation of heart beat. The corresponding histological sections showed apoptotic cells in the embryo proper while the placenta was still intact. In the subsequent process first the embryo and then its membranes disappeared. I also describe in depth, the process of embryonic perishment and the subsequent degradation of the implantation site. Specific markers for macrophages (F4/80), neutrophils (MPo-7), and lymphocytes (B220) were used and apoptotic cells were detected via Caspase 3 staining. The process commenced with the apoptosis of the embryo proper. Early in the gestation (day 8), I observed an inflammatory process located in the decidua capsularis, which led to its disintegration. A massive maternal hemorrhage occurred at the decidua basalis. Degraded material and maternal erythrocytes were found in the uterine lumen. At later gestation (day 9) when the embryo proper has increased in size, the inflammatory process seen on the decidua capsularis resulted in its rupture and the release of the embryo proper into uterine lumen. I suggest that the release of the dead embryo into the uterine cavity occurring between days 9 and 11 of pregnancy might help to escape the immune privileged environment of the implantation site. The degradation of the placenta seems to follow a different pathway.