No Association Was Found Between Mild Iodine Deficiency During Pregnancy and Pregnancy Outcomes: a Follow-up Study Based on a Birth Registry

Abstract

Background Severe iodine deficiency during gestation is associated with adverse pregnancy outcomes; however, the impact of mild-to-moderate iodine deficiency, though prevalent in pregnancy, remains unclear. Methods We extracted follow-up data for 7435 pregnant women from a national iodine deficiency disorders monitoring program from 2016 to 2018 and a mother–child cohort study in 2017 based on a birth registry in Shanghai. Birth outcomes were collected from the registry. Spot urine and household salt samples were collected for iodine testing. Single-factor analysis and logistic regression were used to evaluate the association between maternal iodine status and pregnancy outcomes. Results The median urine iodine level in pregnant women was 137.5 μg/L (interquartile range 82.4–211.5), suggesting mild deficiency according to WHO standards. The incidence of pregnancy termination, preterm birth, congenital malformations, low birth weight, and cesarean section was 3.2%, 4.3%, 1.4%, 2.7%, and 45.2% in the mildly iodine-deficient group and 3.4%, 4.5%, 1.4%, 2.7%, and 44.5% in the normal group, respectively. After adjusting for maternal age and education, trimesters, and preterm birth rate in the general population, the odds ratios for any outcome did not differ significantly between the two groups. Conclusion The present study suggests that mild maternal iodine deficiency is not associated with adverse pregnancy outcomes.

Maternal Iodine Status and Birth Outcomes: A Systematic Literature Review and Meta-Analysis

“…Of these, 53 were identified as potentially relevant after screening of titles and abstracts (with 89% agreement between reviewers) and 26 were identified as relevant following reading of the full texts (with 80% agreement between reviewers). These publications reported on 24 cohorts containing 42,503 participants ( Figure 1 , Supplementary Table S2 ) [ 11 , 12 , 13 , 14 , 16 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ].…”

“… Urinary iodine concentration ( a – c ), iodine to creatinine ratio and birth weight (grams) ( d – f ), dichotomous ( a , d ), linear ( b , e ), and nonlinear ( c , f ) meta-analyses. CI: Confidence interval; Δ: Change in outcome [ 11 , 12 , 13 , 14 , 16 , 28 , 29 , 31 , 33 , 34 , 36 , 37 , 39 , 40 , 41 , 42 , 44 ]. …”

“…Two recent systematic reviews of observational studies of iodine and birth outcomes drew differing conclusions [ 9 , 10 ]. Since these reviews were published, results on iodine and birth outcomes from a number of large birth cohorts have become available, including the Norwegian Mother and Child Cohort Study (MoBa) [ 11 ], the Screening for Pregnancy Endpoints (SCOPE) cohort [ 12 ], the Born in Bradford (BiB) cohort [ 13 ], and results from the Shanghai birth registry [ 14 ]. There is potential for studies in deficient populations to draw substantially different conclusions from those in less-deficient populations, and for effects to only be seen in individuals with particularly poor intakes.…”

A Scoping Review of Iodine and Fluoride in Pregnancy in Relation to Maternal Thyroid Function and Offspring Neurodevelopment

“…I supplementation that began after the 12th wk of pregnancy was associated with significantly low free T4 and a somewhat lower free T3 [ 80 ]. This is supported by a study of women in Tehran ( n = 1286) that found odds of preterm delivery were higher in women with both insufficient and suboptimal thyroid function ( <100 μg/L and TSH ≥ 4 μ /mL) than those with <100 μg/L and TSH <4 μ /mL [ 81 ], and counter to 2 large studies which found mild-to-moderate I insufficiency was not related to worse pregnancy outcomes [ 82 , 83 ]. The final Norwegian study reported a UIC of 79 μg/L and dietary I intake of 140 μg/d, further confirming the I insufficiency of this population [ 84 ].…”

An update: maternal iodine supplementation, thyroid function tests, and child neurodevelopmental outcomes

“…Findings from another 2020 observational study from Tehran showed higher risk of preterm birth in those with deficient UIC and TSH at least 4 mIU/ml [67]. However, two other large observational studies did not find worse pregnancy outcomes associated with MMID [68,69]. A 2023 review of four meta-analysis (MAs) [17,[70][71][72] evaluating the relationship between iodine status and pregnancy and neonatal outcomes suggests a U-shaped correlation between iodine status and maternal and neonatal consequences…”