Association between individual urinary iodine concentrations in pregnant women and maternal/newborn outcomes: a systematic review and meta-analysis.

Objective: To assess whether individual diagnosis of low urinary iodine concentration (UIC) in pregnant women is associated with adverse maternal and neonatal outcomes.

Methods: Studies that compared pregnant women with UIC <150 μg/L and those with UIC 150-249 μg/L were systematically reviewed. MEDLINE, EMBASE, LILACS, and CENTRAL were our source databases. Selection of studies, risk of bias assessment, and data extraction were performed in pairs and independently. Relative risk (RR) with 95% confidence interval (CI) were calculated as an estimate of the effect of iodine <150 μg/L. Stata software was used to perform meta-analyses. The quality of evidence was determined according to the Grading of Recommendations Assessment, Development, and Evaluation.

Results: In total, 7,000 studies were identified, of which 63 were included. With low or very certainty of the evidence, no difference in the incidence of miscarriage (RR: 0.87, 95% CI: 0.64-1.18, 6 studies, 4,855 participants), maternal hypothyroidism (RR: 1.05, 95% CI: 0.68-1.60, 10 studies, 11,773 participants), preterm birth (RR: 1.20, 95% CI: 0.97-1.48, 13 studies, 15,644 participants), stillbirths (RR: 0.79, 95% CI: 0.34-1.82, 6 studies, 3,406 participants), low birth weight (RR: 1.25, 95% CI: 0.88-1.78, 10 studies, 10,775 participants), and small for gestational age (RR: 1.11, 95% CI: 0.90-1.37, 5 studies, 4,266 participants) was observed between the two groups.

Conclusion: In pregnant women, individual diagnosis of UIC <150 μg/L was not associated with adverse maternal and neonatal outcomes, emphasizing UIC concentration as a limited method to assess individual iodine status during pregnancy.