The relationship between maternal urinary iodine concentration and preterm labor

Background and Aim : Iodine deficiency during pregnancy may be associated with poor obstetricoutcomes. The aim of this study was to investigate the relationship between maternal iodine status withpreterm delivery among pregnant Iranian women, considering their baseline thyrotropin (TSH) status.Methods : We used data from Tehran Thyroid and Pregnancy Study (TTPS); a two-phase population-basedstudy carried out among pregnant women receiving prenatal care in centers, under the coverage of ShahidBeheshti University of Medical Sciences. By excluding participants with overt thyroid dysfunction andthose received levothyroxine, the remaining (n = 1286) were categorized in four groups, according to theirurine iodine status: group 1: urine iodine concentration (UIC)<100 μg/L, group 2: UIC=100–150 μg/L,group 3: UIC=150 - 250 μg/L and group 4: UIC≥250 μg/L. The Primary outcome was preterm delivery.Results : In a total of 1286 pregnant women, median (interquartile range) of UIC was 142.3 (133.6) μg/Land 370 (28.8%), 315 (24.5%), 359 (27.9%) and 242 (18.8%) of pregnant women had UIC levels<100μg/L, 100- 150 μg/L, 150-250 μg/L and≥250 μg/L, respectively. Preterm delivery occurred in 29 (9%), 19(7%), 15 (5%) and 8 (4%), respectively. Generalized Linear Regression model (GLM) demonstrated thatthe odds ratio of preterm delivery was significantly higher in women with urinary iodine<100 μg/L andTSH≥4 μIU/ml than those with similar urinary iodine with TSH<4 μIU/ml [OR: 2.5 (95% CI: 1.1, 10), p =0.024].Conclusion : preterm delivery are increased among those ones with UIC<100 μg/L, with serum TSHconcentrations≥4 μIU/mL. Despite the implementation of iodized salt strategies in Iran, mild iodinedeficiency among our pregnant cohort, indicate that iodine supplementation needs to be implemented forpregnant women. Considering the adverse pregnancy outcomes due to iodine deficiency, especially inwomen with TSH≥4 μIU/mL, monitoring of urinary iodine concentration at the population level and iodinereplacement may be needed during pregnancy, even in areas of iodine sufficiency.

Keywords:

Iodine deficiency , pregnancy , outcomes , Tehran Thyroid and Pregnancy , preterm delivery