In pregnancy terms, the moment of quickening refers to the initial motion of the fetus in the uterus as it is perceive or felt by the pregnant woman. According to the Oxford English Dictionary, to "quicken" means "to reach the stage of pregnancy at which the child shows signs of life." In the twentieth century, ultrasound technology made it possible to see that a fetus is in motion even if the pregnant woman does not yet feel it. This technological development made the concept of "quickening" a bit more complex.