Administered radionuclides in pregnancy.

Radiopharmaceuticals are occasionally administered to pregnant patients either out of clinical necessity or by accident. In recognition of the latter, the Society of Nuclear Medicine recommends pregnancy testing before any procedure that will expose the fetus to >50 mGy. When pregnancy is known, the dose of radionuclide to be employed is kept as low as possible without sacrificing radiographic information. The commonly administered radiopharmaceuticals used for lung, gallbladder, kidney, bone, and bleeding scans are labeled with technetium-99m: all deliver whole fetal doses of <5 mGy. These doses are lower than those known to produce deterministic effects, and are likely to be very conservative, since radionuclide exposure delivers protracted irradiation exposures to the embryo and fetus. The actual deterministic risks will decrease with the magnitude of the protraction as compared with the acute effects of irradiating the embryo and fetus. The probability of late effects is considered sufficiently low not to contraindicate the use of these radiopharmaceuticals when medically required or to raise undue concern when they are accidentally administered.