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Effects of different iodine supplementation strategies on thyroid function in iodine-deficient pregnant women: a meta-analysis.

  • 2026-06-10
  • Frontiers in public health 14
    • Yingying Lv
    • Baiming Jin
    • Jiazhuang Guo
    • Jingshu Bu
    • Chen Chen
    • Yunfeng Han
    • Zhiping Xie
    • Yuehui Jia
    • Siyuan Wan
    • Chunjing Zhang

Study Design

Type
Meta-Analysis
Population
iodine-deficient pregnant women
Methods
Chinese and English literature on iodine supplementation in iodine-deficient pregnant women and its associations with thyroid function indices, Tg, and TV was retrieved from PubMed, Medline, Embase, CNKI, WanFang, and WeiPu databases. Effect sizes were estimated using fixed- and random-effects models, reported as standardized mean difference (SMD), odds ratio (OR), and 95% confidence intervals (CIs).
Funding
Unclear

Background

This study aimed to clarify the association between iodine supplementation and thyroid function indices, as well as secondary outcomes including thyroglobulin (Tg) and thyroid volume (TV), in iodine-deficient pregnant women, accounting for different supplementation regimens and trimesters.

Methods

Chinese and English literature on iodine supplementation in iodine-deficient pregnant women and its associations with thyroid function indices, Tg, and TV was retrieved from PubMed, Medline, Embase, CNKI, WanFang, and WeiPu databases. Effect sizes were estimated using fixed- and random-effects models, reported as standardized mean difference (SMD), odds ratio (OR), and 95% confidence intervals (CIs).

Results

Iodine supplementation was associated with reduced serum TSH and Tg levels in iodine-deficient pregnant women (TSH: SMD = -0.14, 95% CI: -0.23, -0.05; Pz = 0.002; Tg: SMD = -0.22, 95% CI: -0.32, -0.13; Pz < 0.001). Subgroup analyses showed significant TSH reductions in Asian populations, third trimester, daily supplementation, 200-300 μg/d doses, and potassium iodide use (Pz < 0.05). Tg was significantly reduced across all regions, iodine supplementation dosages and methods, second/third trimesters, and daily supplementation subgroups (Pz < 0.05). TV was significantly increased in the Europe subgroup and the until postpartum supplementation subgroup (Pz < 0.01). Egger's test suggested publication bias for TV, but results remained robust after trim-and-fill adjustment.

Conclusion

Standardized iodine supplementation notably reduces serum TSH and Tg in iodine-deficient pregnant women, relieving gestational thyroid dysfunction and optimizing maternal thyroid health. Greater TSH improvements are observed in Asian populations, the third trimester, and those taking 200-300 μg potassium iodide daily.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/view/CRD420261323017, identifier: CRD420261323017.

Research Insights

  • Iodine→Increased Serum Free Thyroxine Levels

    Iodine supplementation was associated with reduced serum TSH and Tg levels in iodine-deficient pregnant women (TSH: SMD = -0.14, 95% CI: -0.23, -0.05; Pz = 0.002)

    Effect
    Beneficial
    Effect size
    Small
    Dose
    varied
  • Iodine→Increased Thyroid Volume

    TV was significantly increased in the Europe subgroup and the until postpartum supplementation subgroup (Pz < 0.01).

    Effect
    Harmful
    Effect size
    Small
    Dose
    varied
  • Iodine→Reduced Thyroglobulin Level

    Iodine supplementation was associated with reduced serum TSH and Tg levels in iodine-deficient pregnant women (Tg: SMD = -0.22, 95% CI: -0.32, -0.13; Pz < 0.001)

    Effect
    Beneficial
    Effect size
    Small
    Dose
    200-300 μg/d
  • Iodine→Reduced Thyroid Volume

    TV was significantly increased in the Europe subgroup and the until postpartum supplementation subgroup (Pz < 0.01). Egger's test suggested publication bias for TV, but results remained robust after trim-and-fill adjustment.

    Effect
    Neutral
    Effect size
    Small
    Dose
    not specified in overall result
  • Iodine→Reduced Thyroid-Stimulating Hormone

    Iodine supplementation was associated with reduced serum TSH and Tg levels in iodine-deficient pregnant women (TSH: SMD = -0.14, 95% CI: -0.23, -0.05; Pz = 0.002)

    Effect
    Beneficial
    Effect size
    Small
    Dose
    200-300 μg/d
  • Iodine→Reduced Thyrotropin Level

    Iodine supplementation was associated with reduced serum TSH ... (SMD = -0.14, 95% CI: -0.23, -0.05; Pz = 0.002)

    Effect
    Beneficial
    Effect size
    Small
    Dose
    200-300 μg/d
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