The first three months of pregnancy is a critical period of embryonic development, brain, heart, blood vessels, facial organs, limbs, and so at this stage shape, a little bit inappropriate drugs or excessive doses of X-ray exposure may result in unintended consequences . So at this stage, dentists mother will try to avoid any form of dental examination, including Xiya. By the third trimester, as easily lead to the outside world to stimulate uterine contraction sensitive, so at that stage, all the same to try to avoid dental checks.