Neonatal thyroid‐stimulating hormone concentrations in northern Sydney: further indications of mild iodine deficiency?

Abstract

Objective:To determine whether thyroid-stimulating hormone (TSH) concentrations in a large sample of neonates meet World Health Organization criteria for an iodine-replete population (< 3% of neonates with whole-blood TSH concentrations > 5 mIU/L), and, in a small subset of neonates, to examine the correlation between maternal urinary iodine and neonatal TSH concentrations. Design: Cross-sectional study of neonatal whole-blood TSH values obtained as part of a routine newborn screening program. Setting: Royal North Shore Hospital (RNSH) in northern Sydney. Participants: Two anonymous samples of neonates born at RNSH (1316 infants born between August 1998 and April 1999 and 1457 infants born between 1 March and 31 December 2000); and 84 infants whose mothers had attended RNSH between September 1998 and August 1999 and supplied a urine sample for iodine measurement. Main outcome measures: Iodine status of neonates (proportion with whole-blood TSH values > 5 mIU/L), and urine iodine concentrations of pregnant women. Results: In the two large population samples of neonates, 8.1% (95% CI, 6.6%-9.5%) and 5.4% (95% CI, 4.3%-6.6%), respectively, had whole-blood TSH values > 5 mIU/L (prevalence range for mild thyroid deficiency, 3%-19%). Comparing the TSH values of the 1316 anonymous infants and the 84 identified infants showed no difference between the proportions with TSH values > 5 mIU/L (8.1% v 10.7%, respectively; P = 0.39). Urine iodine concentrations in the 84 pregnant women indicated borderline mild iodine deficiency. TSH values in their 84 infants were positively correlated with maternal urine iodine concentrations. Conclusions: Our results suggest that the population of northern Sydney may have mild iodine deficiency. However, the expected relationship between maternal MJA 2002; 176: 317-320 urine iodine levels and neonatal TSH concentrations was not found.

Iodine deficiency in Australia: is iodine supplementation for pregnant and lactating women warranted?

“…This indicates moderate iodine deficiency. Similar results have been shown in pregnant women in New South Wales and Tasmania 1 , 3 , 13 , 14 …”

Neonatal blood TSH concentration in Wales (UK): an indicator of iodine sufficiency

“…The limitations of neonatal TSH concentrations to assess population iodine sufficiency have been described .…”

“…In particular, caution has been advised over the use of a set TSH cut‐off . WHO criteria for iodine status do not consider the effect of blood spot TSH assay biases, although in recent years the market has been dominated by one method (Perkin Elmer autoDELFIA ® ) that has been used in the recent publications, making it possible to compare populations more critically. The timing of blood spot sample collection is also an important factor .…”

The impact of iodine supplementation and bread fortification on urinary iodine concentrations in a mildly iodine deficient population of pregnant women in South Australia

“…McElduff et al [9] identified that in two populations of neonates 5–8% of the neonates had mild thyroid deficiency as indicated by a thyroid stimulating hormone (TSH) concentrations of greater than 5 mlU/L. More recently Rahman et al [21] reports that neonatal TSH levels of greater than 5 mlU/L have increased by 5% in the last 5 years.…”