Stage of the Pregnancy

An important consideration for possible health effects is the stage of pregnancy in which the radiation exposure occurred:

• In the first two weeks of pregnancy or the second two weeks from the last menstrual period, the unborn child is resistant to the harmful effects of x rays. Miscarriage is not likely to occur if the radiation dose is less than 500 mSv.
• From the third to the eighth week of pregnancy, the unborn child is in the period of early development but is not noticeably affected with birth defects, pregnancy loss, or growth retardation unless the exposure is above 500 mSv.
• From the eighth to the fifteenth week of pregnancy, the unborn child is sensitive to the effects of radiation on the central nervous system. Growth retardation and mental retardation may occur at doses above 50 mSv. The threshold for an observable reduction in IQ has been estimated to be higher than 300 mSv. General diagnostic studies do not reach these levels and, therefore, these effects are rarely of concern for patients.
• Beyond the twentieth week of pregnancy, when the unborn child is completely developed, it has become more resistant to the developmental effects of radiation. The most important thing is that practically none of the diagnostic radiological procedures will affect an unborn child at this late stage of pregnancy and certainly there is no risk for birth defects or miscarriage from the range of exposures that occur from diagnostic studies.
• According to two national committee studies evaluating the reproductive risk of nonionizing radiation, the risk is minimal, if it even exists. Nonionizing sources included in the studies were electromagnetic fields emitted from computers, microwave communication systems, microwave ovens, power lines, cellular phones, household appliances, heating pads and warming blankets, airport screening devices for metal objects, and diagnostic levels of ultrasound.