High-frequency Ultrasonography Based Early Pregnancy Characterization: A Technique to Study Embryo Implantation and Pregnancy Progression in Pregnant Murine Model

High-frequency ultrasonography imaging uses the principle of transmission of ultrasound waves to the organs and internal structures. These waves get reflected and travel back to the ultrasound machine via the transducer probe.

The machine computes the intensity and distance traveled by these waves to reconstruct an image of the selected organ. To detect pregnancy using ultrasonography, place a newly pregnant, anesthetized mouse in supine position on the monitoring platform.

Apply an ultrasound gel to the abdomen to remove any air, which would affect the signal transmission. Position the probe over the lower abdomen. Locate the bladder, which appears as a dark fluid-filled sac. Move the probe slightly upwards to visualize the uterine horn situated below the kidney.

A uterine horn appears cylindrical and exhibits multiple dense spots, each corresponding to an embryo. In these spots, identify the positions to observe decidualization - a process where the  endometrial lining changes to facilitate implantation. These sites emit intense signals and appear lighter. 

Mark all these points on the uterine horn and measure the distances between them. As the pregnancy proceeds, measure the size of each gestational sac and the fetal pole present inside it. Appropriately sized gestational sacs confirm a viable pregnancy.