Transient congenital hypothyroidism in an iodine-replete area is not related to parental consanguinity, mode of delivery, goitrogens, iodine exposure, or thyrotropin receptor autoantibodies.

OBJECTIVE: To assess transient congenital hypothyroidism (TCH) etiologies in two Iranian cities.

MATERIALS AND METHODS: Cord dried blood spot samples were collected from neonates in Tehran and Damavand. Serum TSH and T4 were measured in those with cord TSH > or =20 mIU/l. Normal serum values at 2-3 weeks of age confirmed transient hyperthyrotropinemia (THT), while persistently abnormal levels revealed congenital hypothyroidism (CH). Normal serum TSH and T4 4-6 weeks after levothyroxine replacement therapy discontinuation at 2-3 yr of age differentiated TCH from persistent CH.

RESULTS: Among 50,409 screened newborns, 9 (1:5601 births) were diagnosed as TCH and compared to 88 full-term neonates (>/=37 weeks' gestation) with THT and 45 normal (cord TSH<20 mIU/l) neonates. At a median age of 11 days, median (range) serum TSH values in TCH, THT, and normal neonates were 36.8 (13-130), 3.6 (0.1-13.3), and 2.9 (0.7-8.0) mIU/l (p<0.0001) and serum T4 values were 97 (36-168), 142 (74-232), and 160 (79-228 nmol/l), respectively (p=0.002). Urinary iodine concentration (UIC) >220 microg/l was observed in 5 (55.6%) of TCH neonates. The occurrence of TCH was not associated with gender, parental consanguinity, mode of delivery, pre- or post-natal consumption of goitrogens and/or thyroid affecting medications, TSH receptor autoantibodies, or neonatal UIC.

CONCLUSIONS: Elevated UIC was the most frequent finding in newborns with TCH but the distribution of excessive UIC was not significantly different among TCH, THT, and normal neonates. Since no other etiologies were found in TCH neonates without elevated UIC values, evaluation of other environmental and/or genetic factors is warranted.