Endocrine Abstracts

It is well established that due to enhanced iodine/thyroxine requirement during pregnancy women with inadequate iodine intake are at high risk of iodine deficiency (ID). However, the relative impacts of mild & moderate ID are yet debated. General population inIndia has been declared iodine-sufficient (93%, vide WHO) but we found 70-90% pregnant women from 3 States, iodine-deficient(UIC <150 mg/l).

Objective: To assess the extent of ID and its impact on TSH & FT4 in pregnant women. Methods. Study design: Epidemiological observational survey. Study subjects drew from rural Himalayan foothills of Uttarakhand, UK (n = 120 longitudinal) & Bihar, BR (n = 432 crisssectional). Blood & urine collected from women 18-45years. Only eligible subjects were included. IEC approval & informed consent were obtained. Using UIC as biomarker of iodine-sufficiency (IS >150 mg/l, WHO) pregnant women were categorised into IS, mild ID(<150-100 mg/l), moderate ID(<100-50 mg/l) and severe ID(<50 mg/l). TSH(mIU/l) and FT4(pmol/l) were determined and compared across categories and States.

Results: UK and BR, both populations attest to complete success of USI outreach in India(Iodised salt usage UK, 97% and BR, 100%, both over 10-20 years). But iodisation was adequate only in 17% of study population in BR. BR population also constituted predominantly moderate to severe ID (UIC<100 mg/l, 56.2%,70%,69.7% in 1st, 2nd, 3rd trimester respectively) as compared to UK which was mostly mildly iodine deficient (UIC<150-100 mg/l, 93%,93%,66% in 1st, 2nd, 3rd trimester respectively). TSH & FT4 did not vary significantly among ID categories. But significantly higher median values and upper IQR cut-offs of TSH were observed in almost all categories of ID, in almost all trimesters in BR population, as compared to UK (due to space restriction only 2 categories are shown in Table 1).TABLE 1 UK: UIC<100 mg/l vs BR: UIC<100 mg/l UK: UIC>150 mg/l vs BR: UIC>150 mg/lHowever, all TSH and FT4 values remained within normal range for the population (2.5-97.5 percentile TSH 0.43-5.9mIU/l) based on 2000 data points from our cohorts. The TSH/FT4 correlation was significantly higher in BR women (r = 0.6-0.8) as compared to UK (r = 0.1-0.4) indicating greater sensitisation of hypothalamo-hypophyseal-thyroid axis.

Conclusion: USI outreach in India is a total success but lacks in iodine fortification. Moderate ID does not impair thyroid function and resultant TSH increase may be physiological homeostasis to achieve euthyroidism, rather than pathophysiological.

Acknowledgement: NABL, NABH, DSIR certified lab facilities of SRHU & Apeejay Stya Group & research grant from SRHU is gratefully acknowledged. SLT is a UGC-Rajiv Gandhi fellowship awardee.