The Kaschin-Beck disease occurs generally in the low selenium environment of China's low selenium areas, and nondisease region is generally distributed in the normal selenium environment. In both environments, the selenium dynamics in the course of fetal growth, is about the same. There is a decreased tendency of selenium content in fetus of five months. The selenium content increases when the fetus is six months. After that it decreases again. It is the lowest with in a month before birth and increases after birth. But in both environments, the changes of selenium content in the fetus are based on the different selenium levels.