IODINE INSUFFICIENCY AND NEONATAL HYPERTHYROTROPINAEMIA IN HONG-KONG

OBJECTIVES 23% of the neonatal hypothyroidism in Hong Kong is transien t. The present study aims to evaluate iodine excretion in healthy preg nant women in Hong Kong and to determine whether iodine insufficiency may occur in the local population to account for the type of neonatal thyroid dysfunction seen in our screening programme. SUBJECTS Pilot sc reening of urinary iodine excretion was determined in 253 healthy preg nant women between 32 and 36 weeks gestation. Fetal and maternal thyro id function in relation to urinary iodine excretion was evaluated in a nother 55 pregnant women who had given birth to infants with cord bloo d TSH greater than or equal to 16 mIU/l (95th percentile of the cord b lood TSH screening programme) and the results were compared to a contr ol group of 160 healthy women whose infants had cord blood TSH <16 mIU /l. RESULTS Using a cut-off value of 0.79 mu mol/l, a level as defined by WHO as iodine deficiency, we found that 35.8% of the pregnant wome n had urinary iodine concentrations below this cut off value. We demon strated that the existence of borderline iodine supply affected the ma ternal and fetal thyroid function as evidenced by (i) a negative corre lation between maternal TSH and urinary iodine concentration, (ii) hig her cord blood TSH in those infants whose mothers had a low urinary io dine concentration as compared to those in whose mothers it was normal , (iii) women who had given birth to infants with cord blood TSH great er than or equal to 16 mIU/l had lower urinary iodine concentrations a nd serum fT4 levels as compared to mothers who had given birth to infa nts with normal cord TSH levels, and their offspring also had higher c ord blood thyroglobulin levels. CONCLUSION Although Hong Kong is not a goitrous area, borderline iodine deficiency exists. lodization of sal t in our community could obviate the necessity for iodine supplements in pregnant women and other at-risk groups.