The Nuclear Regulatory Commission (NRC) publishes guides that provide advice to licensees on how best to satisfy regulatory requirements.  Regulatory Guide (RG) 8.13 discusses the limits on prenatal radiation exposure.

For Illinois, dose to the fetus/embryo is governed by 32 Ill. Adm. Code 340.280.  Section 340.280 states, “[Licensees] shall ensure that the dose equivalent to an embryo/fetus during the entire pregnancy, due to occupational exposure of a declared pregnant woman, does not exceed 5 mSv (0.5 rem).  In addition, if a woman does not notify the administration of the estimated date of conception, Section 340.280 (d) states that, “…the licensee or registrant shall ensure that the dose equivalent to an embryo/fetus, as specified in subsection (b) of this Section, due to occupational exposure of the declared pregnant woman does not exceed 0.5 mSv (0.05 rem) per month, during the remainder of the pregnancy.”

It’s interesting to note that if a woman does not declare her pregnancy in writing, the standard occupational dose limits are applied to her, and not the more restrictive dose limits assigned to a woman with a declared pregnancy. So, if you’re pregnant and you don’t declare, a male member of the public has a lower limit placed on him than that of the effective limit placed on your unborn child – by a factor of 50. (5000 mrem for pregnant undeclared worker versus 100 mrem for a male member of the public).  Dr. Michael Stabin, Ph.D. of Vanderbilt wrote an excellent article about radiation as a carcinogen, and the regulatory contradictions surrounding dose equivalent limits for radiation workers and members of the public.  Be sure to take the test at the bottom of his article.