Prenatal radiation exposure: The exposure of an unborn baby to radiation. Radiation exposure of the fetus can occur when the mother's abdomen is exposed to radiation from outside her body as, for example, by diagnostic X-rays. A pregnant woman may also be exposed to radiation by swallowing or breathing in radioactive materials. From the mother, radioactive materials may pass through the umbilical cord to the baby or concentrate in areas of the mother's body near the womb (such as the bladder) and expose the unborn baby to radiation.
The possibility of severe health effects depends on the gestational age of the unborn baby at the time of exposure and the amount of radiation it is exposed to. Unborn babies are more sensitive to radiation during some stages of pregnancy than others. The health consequences can be severe, even at radiation doses too low to make the mother sick. The consequences for the baby can include growth retardation (stunted growth), congenital malformation (birth defects), and abnormal brain function (developmental delay and mental retardation).
Radiation exposure before birth can also increase the risk of cancer later in life. During the first 2 weeks of pregnancy, the radiation-related health effect of greatest concern is the death of the baby. Large radiation doses to the unborn baby during the more sensitive stages of development -- between weeks 2 and 15 of pregnancy -- can cause birth defects, especially to the brain. Between the 16th week of pregnancy and birth, radiation-induced health effects (aside from cancer) are unlikely unless the unborn baby receives an extremely large dose of radiation. After the 26th week of pregnancy, the radiation sensitivity of the unborn baby is similar to that of a newborn.