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A fetal radiation dose of ≤ 50 milli-Gray (mGy) is associated with negligible risks
Data from observational studies of pregnant survivors of nuclear disasters and experimental studies on animals have shown that, in the first two weeks after conception, the main risk is radiationinduced pregnancy termination, which can occur at a radiation dose of 100-200 mGy. From two weeks after conception until term, a minimum fetal radiation dose of 350-500 mGy is required to cause adverse outcomes such as pregnancy loss, fetal malformations, growth restriction and developmental delay.1 Practice guidelines from the American Congress of Obstetricians and Gynecologists suggest a more conservative threshold of 50 mGy or less during pregnancy to avoid adverse events.2
No single diagnostic procedure exceeds the threshold of 50 mGy
Typical fetal radiation doses from common examinations are shown in Appendix 1 (available at www.cmaj.ca/lookup/suppl/doi:10.1503/cmaj.140901/-/DC1).3 For example, the fetal dose from chest radiographs is less than 0.01 mGy. More than 5000 such radiographs in pregnancy...