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

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.