Occupational and Environmental Agents
Pregnant women may be occupationally or environmentally exposed to a variety of chemicals that are associated with poor reproductive outcomes, including spontaneous abortion, low birth weight, neurologic abnormalities, and congenital anomalies. These chemicals include methyl mercury, lead, polychlorinated biphenyls, polybrominated biphenyls, and organic solvents. Verified human teratogens in this class of agents include methyl mercury and organic solvents. Lead is associated with growth restriction and myelination defects but not gross congenital anomalies. Polychlorinated biphenyls and polybrominated biphenyls are associated with skin discoloration and stillbirth.
Ionizing Radiation
Embryonic or fetal radiation exposure usually results from diagnostic radiologic studies. Diagnostic radiation usually exposes the conceptus to less than 5 cGy (5 rads), depending on the number of radiographs taken and the maternal site examined (Table 6). Any woman who is considering pregnancy and who is exposed to ionizing radiation on the job may wish to have her film badge evaluated more frequently to monitor radiation exposure. She should also wear a badge over the pelvic area for a more precise estimate of potential fetal exposure.
Thyrotoxic (therapeutic) radioisotope (131I) exposure is considerably more hazardous to the fetus than diagnostic studies that use iodine I 121. The fetal thyroid is not susceptible to radioisotope damage before 9-11 weeks of gestation. Dosimetry calculations should be made by experienced professionals, and risks may then be estimated based on isotope and biologic half-lives of the specific agents used and gestational timing of the exposure. Generally, the use of radioisotopes should be avoided during pregnancy. Risks associated with radioisotope iodine exposure during pregnancy include microcephaly, fetal growth restriction, goiter, and hypothyroidism. Risks to the infant include mental retardation and stunted physical growth.
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