3.233 Infertility Temporary reduction in sperm counts have been reported following whole-body doses of radiation of 12 cGy. The threshold for permanent male sterility ranges from 2 to 6 Gy. With doses below this threshold, temporary sterility may persist for prolonged periods (up to 5 years has been reported) the duration of which are related to dase. Permanent sterility can be induced in women by acute doses to the ovary of 3 to 4 Gy; the effective dose varies inversely with age at exposure. 3.2.3.4 Hypothyroidism Single doses of at least 10 Gy of external penetrating radiation are required to sufficiently injure the thyroid tissue as to result in clinically evident hypothyroidism. Internal emitters, specifically radioactive iodines, deposited in the thyroid gland can cause clinically detectable hypothyroidism in adults at internal doses to the gland of approximately 3-3.5 Gy. These dose data are derived primarily from the experience of the Marshall Islands’ population. The thyroid becomes active at approximately eleven weeks post-conception. It and the child’s thyroid having smaller mass than the adult gland, concentrate iodine to a greater extent, and thus are more sensitive to injury from internally deposited radioiodines. Thyroid hypofunction in the fetus and children up to about 10 years of age can result in growth retardation, or cretinism at higher doses. 3.2.4 In Utero Effects Exposure of the pregnant womanto radiation can cause effects in the embryo or fetus that are related to dose, dose rate and the period of gestation. Radiation doses high enough to induce ARSin the motherwill have a similar and possibly greater acute effect per unit dose on her fetus and can result in acute fetal death although she may survive. The effect of exposure to lower doses during the embryonic or pre-implantation period is described as "all or nothing,” indicating that if the embryo survives -- and in the absence of other risk factors ~ it will continue to grow and develop normally. Deterministic effects of fetal ore include non-specific congenital malformations, growth retardation including 10 JUb2 G4