Association between individual urinary iodine concentrations in pregnant women and maternal/newborn outcomes

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

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) was 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.

In total, 7000 studies were identified, of which 63 were included. With low or very low certainty of the evidence, no difference in the incidence of miscarriage (RR: 0.87, 95% CI: 0.64-1.18, 6 studies, 4855 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, 3406 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, 4266 participants) was observed between the two groups.

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