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Table 2 Characteristics and summary of findings of n = 12 studies included investigating associations between maternal urinary iodine assessment and child cognitive outcomes

From: Associations between maternal urinary iodine assessment, dietary iodine intakes and neurodevelopmental outcomes in the child: a systematic review

Author Country Design N Gestational age at urine collection Child age at testing Cognitive tests Urinary iodine assessment UIC and/or ICr Association to cognitive outcomes Quality
Bath, S.C. et al., 2013 [6] UK Prospective cohort 1040 mother child pairs ~ 13 weeks gestation 8–9 years WISC; Neale Analysis of Reading Ability. ICPMS: 91.1 μg/L UIC & ICr: 110 μg/g Offspring of women with ICr < 150 μg/g had scores in lowest quartile (OR 1·58, 95% CI 1·09–2·30; p = 0·02), reading accuracy (1·69, 1·15–2·49; p = 0·007), and reading comprehension (1·54, 1·06–2·23; p = 0·02) 9
Markhus, M.W. et al., 2018 [20] Norway Prospective cohort 851 mother child pairs 23.7 weeks 6.1, 12.2 and 18.4 months BSID-III ICPMS: 78 μg/L
n = 155 women reported supplement use with UIC higher 92 μg/L
UIC < 100 μg/L associated with poorer receptive (p = 0.025) and expressive language skills (p = 0.002).
Iodine-containing supplements was associated with lower gross motor skills (b = −0.18, 95% CI = − 0.33, − 0.03, p = 0.02),
9
Van Mil, N.H. et al., 2012 [21] The Netherlands Prospective cohort 1156 mothers and 692 children 13.2 weeks 4 BRIEF-P Ammonium persulfate: 203 μg/g ICr (median)
Supplement use in 27.1% of women with urinary iodine <10th percentile and 30.8% >10th percentile
Offspring of women with low urinary iodine scores had higher scores on the problem scales of inhibition [b = 0.05 (95% CI: 0.01, 0.10), P = 0.03] and working memory [b = 0.07 (95% CI: 0.02, 0.12), P = 0.003]. 9
Hynes, K.L. et al., 2013 [19] Australia Longitudinal follow up 433 mothers and 228 offspring Mean 24.6 weeks (8–41 weeks range) 9 NAPLAN and SARIS tests Kolthoff method:
Median UIC 81 μg/L
71.1% mothers had UIC < 150 μg/L
29.9% mothers had UIC > 150 μg/L
Maternal UIC < 150 μg/L had offspring with 10% reductions in spelling (95% CL 68.0 to 14.3; p = 0.003), 7.6% in grammar (95% CI 60.2 to 1.7, P = 0.038), and 5.7% in English-literacy (95% CI, 0.63 to 0.03; P = 0.034) performance compared to maternal UIC > 150 μg/L. 9
Hynes, K.L. et al., 2017 [18] Australia Longitudinal follow up 449 mothers and 266 offspring Mean 23.7 weeks (6–41 weeks) 13–14 years NAPLAN tests Kolthoff method:
Median UIC 83.2 μg/L
Maternal UIC < 150 μg/L had offspring exhibiting persistent reductions in spelling from Year 3 (95% CL −65.1 to −17.6; p = 0.001)) to Year 9 (95% CL − 57.0 to − 6.2, p = 0.015)) compared to maternal UIC ≥ 150 μg/L. 8
Abel, M.H. et al., 2017 [22] Norway Prospective cohort 53′360 mother-child pairs (19′086 for ADHD score) 18 (n = 1950 for UIC measurements) 9.9 (median) ADHD Rating Scale ICPMS:
Median UIC 61 μg/L (n = 1950 for non-supplement users); 86 μg/L (n = 988 for supplement users)
NS 9
Abel, M.H., et al., 2018 [23] Norway Prospective cohort 39,471 mother child pairs 0–22 (wk. 18 for UIC, n = 2001) 8 CCCS; Vineland Adaptive Behaviour Scale; Performance tests for reading, writing and maths. ICPMS: Median UIC 67 μg/L; 95 μg/L in supplement users and 59 μg/L in non-supplement users. NS 9
Murcia, M. et al., 2017 [24] Spain Prospective cohort 2644 women recruited and 1803 children 13.5 4.8 MSCA Paired-ion reversed-phase HPLC: 123 μg/L UIC (median) and ICr 151 μg/g NS 9
Zhou, S.J. et al., 2018 [25] Australia Prospective cohort 699 mother child pairs < 20 and 28 19.5 months BSID-III Sandell-Kolthoff UIC 186 μg/L NS 9
Cromie, K.J. et al., 2020 [26] UK Prospective cohort 6955 mothers 26–28 weeks 8–12 years ASD Diagnosis through CTV3 read code ICPMS: Median (inter-quartile range) UIC was 76 μg/L (46, 120) and ICr was 83 μg/g (59, 121) NS 9
Ghassabian, A. et al., 2014 [27] The Netherlands Prospective cohort 1525 mother-child pairs < 18 weeks gestation 6 years Non-verbal IQ and language comprehension Ceri-arsenite reaction: median UIC creatinine = 229.6 μg/g (whole sample)
< 150 μg/g median was 119.3 μg/g (12.3%) and > 150 μg/g was 322.9 μg/g
NS 9
Threapleton, D.E. et al., 2020 [28] UK Prospective cohort 6971 mothers5745 children 26–28 weeks gestation 4–7 years EYFS, phonics, and KS1 learning outcomes/social/behavioural difficulties, and sensorimotor control Jaffe reaction: Median (interquartile range) UIC was 76 μg/L (46, 120), and ICr was 83 μg/g (59, 121). NS 9
  1. UK United Kingdom, WISC Wechsler Intelligence Scale for Children, UIC Urinary Iodine Concentration, ICr Iodine Creatine Ratio, ICPMS Inductively Coupled Plasma Mass Spectrometry, CI Confidence Intervals, NS No Significance, BSID-III Bayley’s Scale of Infant Development, BRIEF-P Behavior Rating Inventory of Executive Function, NAPLAN National assessment program-Literacy and Numeracy, SARIS Student Assessment and Reporting Information System, ADHD Attention-Deficit Hyperactivity Disorder, CCCS The Children’s Communication Checklist-short, IQ Intelligence Quotient, MSCA McCarthy Scales of Children’s Abilities, HPLC High Performance Liquid Chromatography, ASD Autism Spectrum Disorder, EYFS Child school achievement Early Years Foundation Stage, KS1 Key Stage One