Response to Letter to the Editor from Levie et al: “Association of Maternal Iodine Status With Child IQ: A Meta-Analysis of Individual Participant Data”

Levie, Deborah; Bath, Sarah C.; Dineva, Mariana; Tiemeier, Henning; Rayman, Margaret P.; Guxens, Mònica; Peeters, Robin P.; Korevaar, Tim I M

doi:10.1210/clinem/dgaa365

Cited by 2 publications

(2 citation statements)

References 7 publications

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“…In contrast to both findings, a previous meta-analysis of three population-based birth cohorts assessing the impact of maternal iodine status on thyroid function indices failed to show an association between urinary iodine and either TSH or free thyroxine levels. 16 It is worth noting that neither thyroxine treatment nor maternal iodine status was ultimately related to neurodevelopmental outcomes in offspring included in this analysis.…”

Section: Discussionmentioning

confidence: 97%

Association of Mild Iodine Insufficiency during Pregnancy with Child Neurodevelopment in Patients with Subclinical Hypothyroidism or Hypothyroxinemia

Casey,

Mele,

Peaceman

et al. 2024

Am J Perinatol

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Objective Our objective was to evaluate whether iodine status in pregnant patients with either subclinical hypothyroidism or hypothyroxinemia in the first half of pregnancy is associated with measures of behavior and neurodevelopment in children through the age of 5 years. Study Design This is a secondary analysis of a multicenter study consisting of two randomized, double-masked, placebo-controlled treatment trials conducted in parallel. Patients with a singleton gestation before 20 weeks' gestation underwent thyroid screening using serum thyrotropin and free thyroxine. Participants with subclinical hypothyroidism or hypothyroxinemia were randomized to levothyroxine replacement or an identical placebo. At randomization, maternal urine was collected and stored for subsequent urinary iodine excretion analysis. Urinary iodine concentrations greater than 150 μg/L were considered iodine sufficient, and concentrations of 150 μg/L or less were considered iodine insufficient. The primary outcome was a full-scale intelligence quotient (IQ) score at the age of 5 years, the general conceptual ability score from the Differential Ability Scales-II at the age of 3 if IQ was not available, or death before 3 years. Results A total of 677 pregnant participants with subclinical hypothyroidism and 526 with hypothyroxinemia were randomized. The primary outcome was available in 1,133 (94%) of children. Overall, 684 (60%) of mothers were found to have urinary iodine concentrations >150 μg/L. Children of iodine-sufficient participants with subclinical hypothyroidism had similar primary outcome scores when compared to children of iodine-insufficient participants (95 [84–105] vs. 96 [87–109], P adj = 0.73). After adjustment, there was also no difference in IQ scores among children of participants with hypothyroxinemia at 5 to 7 years of age (94 [85 – 102] and 91 [81 – 100], Padj 1/4 0.11). Treatment with levothyroxine was not associated with neurodevelopmental or behavioral outcomes regardless of maternal iodine status (p > 0.05). Conclusion Maternal urinary iodine concentrations ≤150 μg/L were not associated with abnormal cognitive or behavioral outcomes in offspring of participants with either subclinical hypothyroidism or hypothyroxinemia. Key Points

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Section: Discussionmentioning

confidence: 97%

Association of Mild Iodine Insufficiency during Pregnancy with Child Neurodevelopment in Patients with Subclinical Hypothyroidism or Hypothyroxinemia

Casey,

Mele,

Peaceman

et al. 2024

Am J Perinatol

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“…The thyroid can store iodine for ∼3 mo for thyroid hormone production ( 59 ), thus the prepregnancy iodine status may be important for coping with the mechanisms of increased demand for thyroid hormone synthesis during pregnancy ( 60 ). To date, no RCTs with supplementation starting preconception have been published, and few observational studies have included prepregnancy iodine status.…”

Section: Discussionmentioning

confidence: 99%

Iodine Nutrition and Iodine Supplement Initiation in Association with Thyroid Function in Mildly-to-Moderately Iodine-Deficient Pregnant and Postpartum Women

Næss

Markhus

Strand

et al. 2021

The Journal of Nutrition

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Background Whereas the adverse effects of severe iodine deficiency during pregnancy are well documented, the effects of mild-to-moderate deficiency are not well established. Objectives We aimed to explore whether iodine nutrition and timing of iodine supplement initiation are associated with thyroid function in pregnant and postpartum women. Methods In this cohort study, 137 pregnant women were enrolled and followed up at gestational weeks (GWs) 18 and 36, and 3 and 6 mo postpartum. Thyroid function tests [thyroid-stimulating hormone (TSH), free triiodothyronine (fT3), and free thyroxine (fT4)], urinary iodine and creatinine concentration (UIC:Cr), and iodine intake (including iodine supplement use) were measured at each time point. The associations between thyroid hormone concentrations and UIC:Cr, iodine intakes, and iodine supplement use were estimated using multiple generalized estimating equation models. Results The median UIC at GW18 was 94 μg/L, indicating mild-to-moderate iodine deficiency. UIC:Cr (β; 95% CI) per 100 μg/g was negatively associated with fT3 (−0.191; −0.331, −0.051) and fT4 (−0.756; −1.372, −0.141) concentrations. Iodine intake (β; 95% CI) per 100 μg/d was positively associated with TSH (0.099; 0.022, 0.177), and negatively associated with fT3 (−0.084; −0.0141, −0.027) and fT4 (−0.390; −0.599, −0.182) concentrations. Compared with no use of supplement, those initiating an iodine-containing supplement prepregnancy and continuing through pregnancy had lower TSH (estimated means) (1.35 compared with 1.68 mIU/L, P = 0.021), and higher fT3 (4.48 compared with 4.28 pmol/L, P = 0.035) and fT4 (15.2 compared with 14.4 pmol/L, P = 0.024) concentrations. Conclusions Lower iodine availability during pregnancy and postpartum was associated with lower TSH, and higher fT3 and fT4 concentrations. The use of an iodine-containing supplement that was initiated prepregnancy and continuing through pregnancy was associated with lower TSH, and higher fT3 and fT4 concentrations, which may suggest improved thyroid function. These findings support the notion that optimization of iodine intake should start before pregnancy. This trial was registered at clinicaltrials.gov as NCT02610959.

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Response to Letter to the Editor from Levie et al: “Association of Maternal Iodine Status With Child IQ: A Meta-Analysis of Individual Participant Data”

Cited by 2 publications

References 7 publications

Association of Mild Iodine Insufficiency during Pregnancy with Child Neurodevelopment in Patients with Subclinical Hypothyroidism or Hypothyroxinemia

Association of Mild Iodine Insufficiency during Pregnancy with Child Neurodevelopment in Patients with Subclinical Hypothyroidism or Hypothyroxinemia

Iodine Nutrition and Iodine Supplement Initiation in Association with Thyroid Function in Mildly-to-Moderately Iodine-Deficient Pregnant and Postpartum Women

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