Etiologies of transient congenital hypothyroidism in Tehran and Damavand

The incidence of permanent and transient congenital hypothyroidism (CH) has been previously reported. This report illustrates the causes of transient CH. From February 1998 to August 2002, cord spot samples were collected on filter papers in Tehran and Damavand hospitals and TSH  20 mU/L (two-site IRMA) were recalled. Between 7-14 days of life or thereafter, serum values of TSH > 10 mU/L and T4 < 6.5 g/dL were considered as CH. After taking the history of maternal ingestion of thyroid affecting drugs and goitrogens during pregnancy and perinatal period, CH-affected newborns were underwent thyroid scanning (99mTC) and eutopic cases were followed up until May 2003. Discontinuation of L-T4 for four weeks and normal serum TSH and T4 values determined transient CH. Maternal and neonatal serum were assayed for thyrotropin receptor autoantibodies (TRAb) and their urine samples were assayed for iodine concentrations. Of 35067 neonates, 373 were recalled (1.06%), 35 had CH (1:1002 births), and 6 had transient CH (1:5845 births). Median urinary iodine concentration in CH neonates (n=26) and their mothers (n=25) was 363 (range 70-500) and 200 (72-410) g/L, respectively. The history of maternal ingestion of thyroid affecting drugs was negative and of goitrogens was minimal. Serum TRAb levels were normal. All mothers were exposed to iodinated disinfectants during perinatal period. Iodine excess (410-500 g/L) was detected in three cases with transient CH. Undue usage of iodinated disinfectants during perinatal period can result in transient CH in the offspring and should be prevented.