Pregnant women should not normally be given X-rays because they can expose the unborn baby to direct X-ray beams, according to the U.S. Food and Drug Administration. X-rays of the mother's abdomen, pelvis, stomach, kidneys and lower back should be avoided in particular.

An unborn baby is very sensitive to the effects of radiation because while it's in the uterus, cellular division rapidly takes place, and these nascent cells grow into tissues and specialized cells. When these cells are exposed to radiation, the risk of birth defects or future illness, such as leukemia, may be increased.

Most diagnostic X-rays involving the head, teeth, chest, arms or legs do not expose the mother's reproductive organs to the harmful effects of radiation, according to the Mayo Clinic. The usual dose of radiation that is associated with a traditional X-ray, even if done on the pelvis or abdomen, still does not pose a great risk to the unborn child. After the 20th week of pregnancy, the fetus becomes more resistant to the effects of radiation. At this stage, the fetus may not be any more vulnerable to the effects of radiation than the mother is during the late stages of pregnancy, according to the Health Physics Society.