Abstract
BackgroundEmbryo resorption is a major problem in human medicine, agricultural animal production and in conservation breeding programs. Underlying mechanisms have been investigated in the well characterised mouse model. However, post mortem studies are limited by the rapid disintegration of embryonic structures. A method to reliably identify embryo resorption in alive animals has not been established yet. In our study we aim to detect embryos undergoing resorption in vivo at the earliest possible stage by ultra-high frequency ultrasound.MethodsIn a longitudinal study, we monitored 30 pregnancies of wild type C57BI/6 mice using ultra-high frequency ultrasound (30-70 MHz), so called ultrasound biomicroscopy (UBM). We compared the sonoembryology of mouse conceptuses under spontaneous resorption and neighbouring healthy conceptuses and correlated the live ultrasound data with the respective histology.ResultsThe process of embryo resorption comprised of four stages: first, the conceptus exhibited growth retardation, second, bradycardia and pericardial edema were observed, third, further development ceased and the embryo died, and finally embryo remnants were resorbed by maternal immune cells. In early gestation (day 7 and 8), growth retardation 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 was transformed into echodense tissue surrounded by fluid filled caverns. In corresponding histologic preparations, fibrinoid material interspersed with maternal granulocytes and lacunae filled with maternal blood were observed. In later stages (day 9–11) resorption prone embryos were one day behind in their development compared to their normal siblings. The space between Reichert’s membrane and inner yolk sac membrane was enlarged The growth retarded embryos exhibited bradycardia and ultimately cessation of heart beat. Corresponding histology showed apoptotic cells in the embryo while the placenta was still intact. In the subsequent resorption process first the embryo and then its membranes disappeared.ConclusionsOur results provide a temporal time course of embryo resorption. With this method, animals exhibiting embryo resorption can be targeted, enabling the investigation of underlying mechanisms before the onset of total embryo disintegration.
Highlights
Embryo resorption is a major problem in human medicine, agricultural animal production and in conservation breeding programs
In our study we described the in vivo process of murine embryo resorption using ultrasound biomicroscopy (UBM) and correlated our ultrasound data to histology
On the basis of our study growth retardation can be strongly associated with the resorption process, even though a considerable variability in developmental stage within one litter has been demonstrated in the post mortem study of Thiel et al [25]
Summary
Embryo resorption is a major problem in human medicine, agricultural animal production and in conservation breeding programs. To yield a reliable result on the actual rate of resorption in post mortem studies, high animal numbers are needed to systematically evaluate every day of pregnancy. In studies on early embryo loss, among hundreds of implantation sites, only one conceptus was either not completely normal, or completely destroyed but in a state of early resorption [10]. This fact is a major concern for the investigation of feto-maternal immune interactions, where cause and effect are especially difficult to distinguish
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