These scanners work in two ways. One type uses nonionizing electromagnetic radiation (millimeter waves), a form of energy similar to that used in radar images and radio signals. This type of radiation, which has been used for a century, has no known health effects. The other type of scanner uses "back scatter" ionizing radiation, which exposes an individual to a very weak X-ray signal. The radiation emitted from the scanner is weak enough that the X-ray doesn't penetrate the body. With either type of machine, there's no evidence of risk to the developing fetus. The risk to the mother, even with repeated exposures, would be immeasurably small.