Although the lining of the uterus is relatively thin, the ability to get pregnant indicates that the fertilized egg has found a suitable location to settle, grow, develop and check that the pregnancy has taken place within the uterus and that bleeding will not occur. Bleeding can only occur when the progesterone in the body decreases or when other corresponding symptoms occur, for example, due to overwork or sex, which may lead to bleeding. The main reason is that external stimuli can cause the uterus and the gestational sac to peel off from each other, which will lead to bleeding, and it has nothing to do with the thinness of the uterine lining. If the lining of the uterus is relatively thin, the fertilized egg will often not be able to implant and become pregnant.