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National Council on Radiation Protection and Measurements (NCRP) Report No. 174, Preconception and Prenatal Radiation Exposure: Health Effects and Protective Guidance, updates and expands NCRP Report No. 54, Medical Radiation Exposure of Pregnant and Potentially Pregnant Women (1977). Scientific knowledge has increased and public concerns have changed in the 36 years since NCRP Report No. 54 was published. The scope of NCRP Report No. 174 covers both ionizing radiation sources and specific nonionizing sources (i.e., magnetic-resonance imaging [MRI], ultrasound imaging, and radiofrequency [RF] fields).

This report provides information on the types, sources, and magnitudes of ionizing radiation exposures of reproductive relevance. Ionizing radiation exposures from medical care (diagnostic and therapeutic procedures, including radiopharmaceuticals) are addressed as well as from occupational sources, common environmental exposures, and accidental or deliberate (e.g., a terrorist act) releases of radionuclides. The ionizing radiation sources discussed consist predominantly of low linear energy transfer (LET) radiation (e.g., x rays from prenatal medical procedures).

The risks from ionizing radiation exposure are examined in detail from preconception through pregnancy and during the nursing of infants. Outcomes and associated risks from preconception exposure that were evaluated include infertility, stillbirths, birth defects, genetic alteration, and cancer. Outcomes and associated risks from exposure during pregnancy that were evaluated include congenital malformations, growth retardation, embryonic and fetal death, mental retardation and neurobiological effects, and cancer.

Also discussed is the risk to the nursing infant from the transfer of radioactive material through the mother's milk (e.g., milk from a mother who received a radiopharmaceutical) as well as from direct exposure due to radionuclides present in the mother's body. Methods for managing dose and reducing risk from various medical procedures are also addressed.

For nonionizing sources (MRI, ultrasound imaging, and RF fields), the focus is on prenatal exposure, with limited coverage of childhood and adult exposure. Outcomes and associated risks during pregnancy that were evaluated, as relevant to exposure from a particular nonionizing source, include low birth weight, delayed speech, dyslexia, nonright-handedness, and impaired intellectual performance.

Effective methods of counseling and communicating the various risks are described, along with examples of consultations concerning risk prior to and during pregnancy. In particular, the report provides specific conclusions and recommendations concerning the health effects discussed and associated protective guidance.

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