[The chambers of the bovine uterus during early pregnancy. A comparative morphologic, sonographic and nuclear spin...

In the bovine, the uterus shows prominent circular folds during early pregnancy. These folds protrude into the lumen nearly at right angles to the uterine wall and, reaching a height of about 2-3 cm in some cases, often reach the center of the uterine lumen. Thus the uterus becomes apparently divided into a number of pocket-like chambers. Endometrial folds are usually found in the pregnant as well as the contralateral uterine horn. Intra-uterine features can be well demonstrated on exenterated bovine uteri without injuring the organ by means of nuclear magnetic resonance imaging with a high resolution performance. This technique was used to examine the uteri of 4 heifers on day 26, 28, 32 and 55 of pregnancy, respectively. The 3-dimensional imaging of these uteri demonstrated the presence of crescent-shaped folds usually at right angles to the long axis of the uterine horn. These endometrial folds explain why the allantochorionic vesicle cannot be demonstrated in toto by transrectal sonography during early pregnancy, apparently being subdivided by the protrusions from the uterine wall. It has been found that the uterus is characterized by 2-3 echo-weak compartments around day 25 of pregnancy and by about 4-6 by day 30. The number may yet increase with progressing pregnancy. Histological sections out of the wall of the pregnant and the contralateral uterine horn have revealed that the folds are composed mainly of the endometrium (Tunica mucosa) and the circular muscle (Stratum circulare).