radioactive iodine thyroid ablation has been shown to be an inexpensive , safe , and effective treatment for hyperthyroidism .
it is the most commonly used method for treating adult patients with graves ' disease .
special precautions must be used in women of child - bearing age because of the possible detrimental side effects of fetal exposure .
the american college of radiology ( acr ) practice guideline for the performance of therapy with unsealed radiopharmaceutical sources states that pregnancy should be ruled out using one of the following four criteria : ( 1 ) a negative hcg test obtained within 72 hours prior to administration of the radiopharmaceutical , ( 2 ) documented history of hysterectomy , ( 3 ) a postmenopausal state with absence of menstrual bleeding for two years , and ( 4 ) premenarche in a child age of 10 years or younger .
the society of nuclear medicine ( snm ) procedure guideline for therapy of thyroid disease with i-131 states that females of child - bearing age should routinely be tested for pregnancy within 72 hours or less before i-131 treatment .
when the patient 's history clearly indicates that pregnancy is impossible , the treating physician may omit the pregnancy test .
tj ( not the patient 's initials ) is an adult female diagnosed with graves ' disease , which was treated with i-131 therapy in december 2004 .
she had been doing well until june 2006 when she presented to the pediatric endocrinology clinic with reoccurrence of her disease .
her thyroid function tests showed tsh < 0.03 ( normal 0.325.0  munit / ml ) , free t4 2.80 ( normal 0.711.85  ng / dl ) , and t4 19.1 ( normal 5.012.0  mcg / dl ) .
tj was scheduled for a radioactive iodine uptake and scan with subsequent ablation with i-131 .
a qualitative urine pregnancy test was performed 24 hours prior to ablation and was negative .
a radioiodine uptake and scan revealed a 24-hour uptake of 100% ( normal 10%30% ) . informed consent for i-131 therapy was obtained .
tj verified that she was not pregnant and was given an activity of 19.8  mci of i-131 .
approximately four months later , after slipping and falling at work , tj presented to her physician with a complaint of low back pain . magnetic resonance imaging ( mri ) of her lumbar spine revealed an intrauterine pregnancy .
it was estimated that the fetus was eight to ten days old at the time of i-131 treatment .  
neonatal thyroid function tests revealed suppressed tsh ( < 0.02 , normal 0.325.0  munit / ml ) , elevated t4 ( 24.4 , normal 5.012.0  mcg / dl ) , and free t4 ( 4.54 , normal 0.581.64  ng / dl ) .
in addition , the infant had an elevated thyroid receptor antibody ( trab ) titer of 82% ( negative < 10% , intermediate 10%15% , positive > 15% ) . based on the laboratory evaluation ,
because he was asymptomatic , a decision was made not to treat but to monitor him closely . over the next six months
his thyroid function tests normalized with tsh 0.73  munit / ml , t4 10.3  mcg / dl , free t4 1.11  ng / dl , and trab < 15% .
thyroid embryogenesis is largely completed by 1012-week gestation .   at 10-week gestation , the thyroid gland is able to trap and concentrate iodine and synthesize thyroid hormones thyroxine and triiodothyronine .
after 10-week gestation , significant exposure to the fetal thyroid can occur from therapeutic doses to the mother , resulting in hypothyroidism and cretinism .
there have been no reports of birth defects or childhood malignancy in children born to the mothers who received radioactive iodine for graves ' disease before the 10th week of pregnancy .
we believe the infant 's thyroid gland was not affected by the i-131 therapy because he was exposed prior to 10-week gestation . quantifying the
exact absorbed dose by the embryo in this case is difficult and depends on many variables .
this calculation likely overstates the actual absorbed dose , as the model assumes that i-131 crosses the placenta . in this case , due to the placenta being in the early stages of development during the second week of gestation
it is estimated that the embryo absorbed dose with i-131 treatment in early pregnancy is 0.072  mgy / mbq .
our patient received a dose of 19.8  mci ( 732.6  mbq ) , which corresponds to an absorbed dose of approximately 5.3  rads after converting from gy to rads .
deterministic effects are those that are known to occur at a given radiation threshold . for example , if a patient were to receive an acute dose of 2  gy to the lens of the eye , the patient will develop a cataract .
stochastic effects are those that can theoretically occur at any radiation dose . for example , any radiation dose could potentially induce a cancer in the future . the probability of a stochastic effect increases as dose increases , but there is no radiation threshold dose below which one can say a stochastic effect will not occur . therefore , stochastic effects can theoretically occur with any radiation dose .
the only known deterministic effect of radiation at an absorbed dose of less than 10  rads is possible spontaneous abortion at 114 days postconception .
based on the data above , this dose level ( 10  rads ) was not reached in this patient . on the other hand ,
thus , the radiation dose to any developing embryo should be minimized , and it is reasonable to ascertain an accurate pregnancy test prior to the use of i-131 therapy .
studies have demonstrated that the risk of congenital effects have been negligible at doses of 5  rads or less when compared to other risks of pregnancy .
in addition , the risk of malformation only significantly increases at doses above 15  rads .
mental retardation has been shown to occur in the offspring of pregnant mothers ; however , it is at doses greater than 20  rads and generally after the eighth week of gestation . a screening study of thyroid cancer among individuals exposed to in utero i-131 from the chernobyl fallout , however , did demonstrate an increased risk of thyroid carcinoma approximately 20 years after the accident .
thus , our estimation that the infant was exposed to approximately 5  rads supports that no deterministic effects should have occurred , but one can not exclude the future potential for stochastic effects .  
as previously stated , the acr practice guideline for the performance of therapy with unsealed radiopharmaceutical sources states that pregnancy should be ruled out using one of the following four criteria : ( 1 ) a negative hcg test obtained within 72 hours prior to administration of the radiopharmaceutical , ( 2 ) documented history of hysterectomy , ( 3 ) a postmenopausal state with absence of menstrual bleeding for two years , and ( 4 ) premenarche in a child age 10 or younger . the snm procedure guideline for therapy of thyroid disease with i-131 states that females of child - bearing age should routinely be tested for pregnancy within 72 hours or less before i-131 treatment .
when the patient 's history clearly indicates that pregnancy is impossible , the treating physician may omit the pregnancy test .
neither of the above guidelines specifies whether the pregnancy tests should be quantitative or qualitative .
typically , serum pregnancy tests are more sensitive than standard urine pregnancy tests because the serum concentration of hcg is significantly higher than its urine concentration .
detection of hcg in maternal serum is evident only after implantation and vascular communication has been established with the decidua by the syncytiotrophoblast , which occurs 810 days following conception .  
serum hcg can be detected in about 5% of patients eight days after conception and about 98% of patients by 11 days postconception .
in contrast , urine pregnancy tests will be positive 1517 days after conception in 98% of patients [ 14 , 16 ] .
this rule suggests that radioactive iodine therapy only be administered during the 10 days after the onset of the menstrual period .
however , this protocol may not be effective if the patient has irregular menstrual cycles .
one possible suggestion is to incorporate the ten day rule protocol into the current guidelines for patients who have regular 28-day menstrual cycles . for patients with irregular cycles or who require immediate ablation , quantitative serum hcg pregnancy tests on the day of the treatment
should be considered .   because serum hcg is detected in 98% of pregnant patients by day 11 , recommending the patients to abstain from sexual activity for at least two weeks prior to i-131 therapy may be suggested .
this abstinence would cover the gap from the time of conception to the time the serum hcg test becoming positive .
however , the physician would have to rely on the patient for providing an accurate menstrual cycle and sexual history .
it is imperative to rule out pregnancy prior to the administration of radioactive iodine therapy due to the potential detrimental side effects of fetal exposure .
the dose of i-131 in this particular case would be unlikely to result in any deterministic events .
however , under the premise that any unnecessary exposure to radiation is important in preventing any potential stochastic events , an accurate pregnancy screening protocol may be warranted in preventing inadvertent i-131 treatment in early pregnancies of women with graves ' disease .
the current acr and snm guidelines only mandate a hcg test being obtained within 72 hours prior to the treatment .
this approach may miss a small number of pregnancies as a serum or urine pregnancy test does not become positive until implantation occurs , which happens 810 days postconception . though we recommend re - evaluating the acr and snm guidelines for future clarifications
, it is possible that despite combining the patient 's history , the ten day rule and the hcg screening , an unsuspected pregnancy may be missed .
 graves ' disease is a thyroid - specific autoimmune disorder in which the body makes antibodies to the thyroid - stimulating hormone receptor leading to hyperthyroidism . 
 therapeutic options for the treatment of graves ' disease include medication , radioactive iodine ablation , and surgery . 
 radioactive iodine is absolutely contraindicated in pregnancy as exposure to i-131 to the fetal thyroid can result in fetal hypothyroidism and cretinism . 
 here we describe a case of a female patient with recurrent graves ' disease , who inadvertently received i-131 therapy when she was estimated to be eight days pregnant . 
 this was despite the obtaining of a negative history of pregnancy and a negative urine pregnancy test less than 24 hours prior to ablation . at birth , 
 the infant was found to have neonatal graves ' disease . 
 the neonatal graves ' disease resolved spontaneously . 
 it was suspected that the fetal thyroid did not trap any i-131 as it does not concentrate iodine until 10 weeks of gestation . 
1. Introduction
2. Case Report
3. Discussion
4. Conclusion