Iodine deficiency during pregnancy: a national cross-sectional survey in Latvia

Abstract

Objective: Low iodine intake during pregnancy may cause thyroid dysfunction, which results in inadequate fetal brain development. In the absence of a universal salt iodization programme, we conducted a nationwide survey of iodine deficiency in pregnant women in Latvia.

Design: A countrywide twenty-cluster survey, with at least twenty women per cluster. Participants completed a questionnaire on dietary habits concerning iodine intake (n 739). Thyroid function (thyroid-stimulating hormone, free thyroxine and thyroperoxidase antibodies) was measured (n 550). Urinary iodine was measured using the ammonium persulfate method (n 696).

Setting: The survey was performed in all regions of Latvia during the spring and autumn seasons in 2013.

Subjects: Pregnant women (n 829).

Results: The median creatinine (Cr)-standardized urinary iodine concentration (UIC) was 80·8 (interquartile range (IQR) 46·1-130·6) µg/g Cr or 69·4 (IQR 53·9-92·6) µg/l during pregnancy, and 81% of pregnant women had UIC levels below the WHO recommended range of 150-250 µg/g Cr. The UIC was lowest during the first trimester of pregnancy, 56·0 (IQR 36·4-100·6) µg/g Cr, reaching higher concentrations of 87·5 (IQR 46·4-141·7) µg/g Cr and 86·9 (IQR 53·8-140·6) µg/g Cr in the second and third trimesters, respectively. Women taking supplements containing ≥150 µg iodine (6·8% of respondents) had non-significantly higher UIC than did women without supplementation (96·2 v. 80·3 µg/g Cr, respectively, P=NS). Thyroperoxidase antibody concentration did not correlate significantly with UIC: Spearman's ρ=-0·012, P=0·78.

Conclusions: The median UIC indicates iodine deficiency in pregnant women in Latvia. Iodine supplementation (150 µg daily) and regular UIC monitoring should be suggested to overcome iodine deficiency and to reach the recommended levels without inducing autoimmune processes.

Keywords: Iodine deficiency; Iodine supplementation; Pregnancy.

Fig. 1

Frequency distribution of iodine excretion among a nationally representative sample of pregnant women (n 696), Latvia, 2013 (UIC, urinary iodine concentration; Cr, creatinine)

Fig. 2

Median iodine excretion during pregnancy trimesters among a nationally representative sample of pregnant women (n 696), Latvia, 2013: (a) UIC (μg/g Cr); (b) UIC (μg/l). Values are medians with interquartile ranges represented by vertical lines; horizontal lines linking bars indicate statistically significant (*P<0·05; **P<0·001) differences between the groups (UIC, urinary iodine concentration; Cr, creatinine; IQR, interquartile range)