The case for fetal dosimetry was established when the link between radiosensitivity and the rate of cellular division/specialization was established by Bergonié and Tribondeau in 1906. One of the most rapidly dividing and unspecialized groups of cells in the body is the developing embryo/fetus. The birth defect risks to the developing embryo/fetus from ionizing radiation exposure include growth restriction, deformities, abnormal brain function, and increased cancer risk later in life. These risks are greatest from weeks 10 to 17 and increase proportionally as the fetal dose increases.

Given these risks, fetal dosimetry establishes a lower dose limit for declared pregnant radiation workers. The dose to the embryo/fetus should not exceed 0.5 rem (5 mSv) over the entire gestation period and the monthly dose rate should be relatively uniform (i.e., it should not exceed 0.5 mSv (50 mrem) in any month once the pregnancy is known).

When is Fetal Dosimetry Required?

Federal regulations [29 Code of Federal Regulations (CFR) Part 1604] recognize that pregnancy is a medical condition that can be debilitating. “Women affected by pregnancy, childbirth, or related medical conditions…” must be treated “…the same as other persons not so affected but similar in their ability or inability to work.” Disparate treatment of pregnant employees is in prima facie violation of Title VII of the Civil Rights Act (i.e., discrimination based on sex, including pregnancy) as decided by the US Supreme Court in United Automobile Workers v. Johnson Controls, 499 U.S. 187 (1991).

Filing a declaration of pregnancy in order to utilize fetal dosimetry dose rates is a radiation worker’s choice; an informed decision based on the risk information and dose results provided by the employer and their understanding of the teratogenic effects of radiation. A declaration of pregnancy must be documented in writing. However, a pregnant radiation worker is not required and cannot be coerced by the employer to declare. If a pregnancy is not declared in writing, the undeclared pregnant employee will continue to be subject to the same radiation dose limits that apply to other radiation workers. A declaration of pregnancy cannot be made for planning purposes (i.e., it is a declaration that you are already pregnant).

Medical proof of pregnancy is typically not required. However, federal regulations do not prohibit employers from asking for such proof and it may be needed to assist an employer in complying with the lower dose limits. State regulations and local policies may prohibit this. If a miscarriage occurs or the declared pregnant employee finds out that they are no longer pregnant, they should inform the Individual Responsible for Radiation Protection (IRRP) or the Radiation Safety Officer (RSO). The lower dose limits for the embryo/fetus will remain in effect until a declared pregnant employee informs their employer that they are no longer pregnant. Your employer’s policy for declared pregnant employees may require a written withdrawal. A declaration of pregnancy can be withdrawn even if the employee remains pregnant.

For contract employees, the facility that monitors the contract employee’s dose must limit the dose to the embryo/fetus when pregnancy is declared. This is typically where the contract radiation worker is exposed to ionizing radiation.  In summary, pregnant radiation workers are responsible for minimizing radiation exposure to the embryo/fetus until they declare their pregnancy in writing.  When the pregnancy is declared in writing, the employer takes an active role to limit fetal dose (e.g., through job modifications).  Declared pregnant employees are responsible to minimize their exposure IAW any job modifications required by the employer. Source – US Nuclear Regulatory Commission Guide 8.13 (Instruction Concerning Prenatal Radiation Exposure), Rev 3, 1999.

Who Receives the Declaration of Pregnancy and What Happens Next?

The employee should complete the Declaration of Pregnancy form according to their facility’s policy. The form is typically returned to the IRRP or the RSO. The pregnant worker should be prepared to provide the IRRP or RSO with the estimated month and year of conception. The IRRP or RSO will discuss the dose you typically receive while performing your job and your estimated dose since the date of conception.

If you have exceeded the 0.5 rem (5 mSv) dose limit from the estimated date of conception to the date of declaration, an additional dose of 0.05 rem (0.5 mSv) is allowed during the remainder of your pregnancy (check your state’s regulations as they may be more restrictive). The IRRP or RSO will ask you if you understand the teratogenic effects of radiation and provide additional instruction/education as needed. A best practice is to provide the facility’s policy for pregnant employees and a copy of US Nuclear Regulatory Guide 8-13 (or the equivalent). While it is typically not required to comply with the lower fetal dose limits for declared pregnant employees, an employer may require you to change your job or job responsibilities [e.g., limiting or eliminating fluoroscopic work, limiting the number or types of nuclear medicine procedures you perform (e.g., Iodine 131 therapy); and/or eliminating portable X-rays, shift work, and on-call/emergent response]. You cannot be terminated for declaring that you are pregnant.

Wearing a Fetal Dosimeter

After completing the declaration of pregnancy form, the IRRP or RSO will assign you a separate fetal dosimeter that will be exchanged monthly. The initial dosimeter you receive to monitor fetal dose may be a spare whole-body dosimeter. The IRRP or RSO will contact LANDAUER to inform them of your estimated date of conception and the date you declared your pregnancy. The IRRP or RSO will assign the additional dosimeter you were issued as a fetal dosimeter and order subsequent fetal dosimeters.

Subsequent fetal dosimeters will have a baby icon on the front and the word “Fetal” on the back, which will allow you to distinguish between the fetal dosimeter and other dosimeters. The fetal dosimeter is to be worn in addition to other dosimeters that you are assigned (e.g., whole-body, collar, ring). Wear the fetal dosimeter centered on the waist (under the protective apron if a protective apron is worn). Verify you are wearing each dosimeter in the proper location by checking the dosimeters for the fetal icon before attaching them to your clothing or a protective apron.

Fetal Dosimetry Monitoring Criteria & Dose Results

A best practice is to monitor all employees who are routinely exposed to ionizing radiation in the course of their employment. However, some facilities have groups of radiation workers that are not monitored (e.g., doctors, nurses, and technologists). Radiation safety training provided to monitored and unmonitored radiation workers must include the biological effects of radiation, risks of teratogenic effects to the embryo/fetus, and the right to declare a pregnancy and receive a fetal dosimeter. Monitoring is required by federal regulation (10 CFR 20.1502, Conditions Requiring Individual Monitoring of External and Internal Occupational Dose) for “Declared pregnant women likely to receive during the entire pregnancy, from radiation sources external to the body, a deep dose equivalent in excess of 0.1 rem (1 mSv).”

Fetal dose results must be maintained with the dose results of the declared pregnant radiation worker. The declaration of pregnancy must also be maintained, but it can be maintained separately. A monthly fetal dose of less than 0.1 rem (1 mSv) is not considered to be a significant variation above a uniform monthly dose rate. However, to maintain the dose within limits and ALARA, the fetal dose should not exceed 0.05 rem (0.5 mSv) in a given month. If a declared pregnant employee exceeds the dose limits, the IRRP or RSO will document the cause and will eliminate tasks where additional occupational exposure is likely during the remainder of the gestation period. Check your state’s regulations to ensure that they mirror these requirements and recommendations. State regulations are often more restrictive.

For more information, see the comprehensive article “Fetal Monitoring: Tracking Radiation Exposure During Pregnancy” or the on-demand fetal dosimetry webinar by Christine Krieman, MS, Practice Associate, Radiation Safety Support Services, Landauer Medical Physics, the US Nuclear Regulatory Commission Guide 8.13, Rev 3, 1999 (Instruction Concerning Prenatal Radiation Exposure), and the US Nuclear Regulatory Commission Guide 8.29, Rev 1, 1996 (Instruction Concerning Risks from Occupational Radiation Exposure).