Can Mild-to-Moderate Iodine Deficiency during Pregnancy Alter Thyroid Function? Lessons from a Mother–Newborn Cohort

Abstract

Severe iodine deficiency during pregnancy has substantial hormonal consequences, such as fetal brain damage. Data on the potential effects of mild-to-moderate iodine deficiency on the thyroid function of pregnant women and their newborns are scarce and divergent. We investigated the association between iodine intake in pregnancy and maternal and neonatal thyroid function in a region with mild-to-moderate iodine deficiency. Pregnant women’s iodine status was evaluated using an iodine food frequency questionnaire, serum thyroglobulin (Tg), and urinary iodine concentration (UIC). Neonatal thyrotropin (nTSH) values were measured after birth. Obstetrics and anthropometric data were also collected. Among the 178 women (median age 31 years) included in the study, median (interquartile range) estimated dietary iodine intake, Tg and UIC were 179 (94–268) μg/day, 18 (11–33) μg/L, and 60 (41–95) μg/L, respectively. There was a significant inverse association of iodine intake with Tg values among the study population (β = −0.2, F = 7.5, p < 0.01). Women with high free triiodothyronine (FT3) values were more likely to exhibit an estimated iodine intake below the estimated average requirement (160 μg/day, odds ratio [OR] = 2.6; 95% confidence interval [CI], 1.1–6.4; p = 0.04) and less likely to consume iodine-containing supplements (OR = 0.3, 95% CI, 0.1–0.8; p = 0.01). It is possible that thyroid function may be affected by iodine insufficiency during pregnancy in regions with mild-to-moderate iodine deficiency. The relatively small sample size of the studied population warrants further investigation.

Does Iodine Intake Play a Role in Modifying the Relationship between Maternal Dysglycemia and Birth Weight?

“…Moreover, the estimated iodine from ICS was 62 µg/day, although the current study participants reported that the majority of ICS they consumed contained 220 µg of iodine per tablet. The reason for this gap is the inconsistent ICS intake values reported by the ICS consumers who participated in our study, resulting in a weighted lower estimate of iodine intake from ICS (Table 2) [16]. In light of this, safe and mandatory iodine prophylaxis in Israel should be urgently implemented.…”

“…The median Tg value determined was 18 µg/L; this is above the cutoff considered for iodine sufficiency in pregnancy, indicating iodine insufficiency (>13 µg/L) in this study population [25]. Detailed nutritional, hormonal, and clinical characteristics of the study population were previously described [16].…”

“…The relatively low proportion of participants presenting a sufficient iodine status (Tg < 13 µg/L, 68%, Table 1) [25] along with the high proportion of participants reporting an inadequate iodine intake below the EAR (160 µg/day, 41%, Table 2) [20] and levels that might correspond to the iodine status of cases of severe ID according to UIC (<50 µg/L, Table 2) [23,24] should all raise concerns for public health. Two major reasons may explain this ongoing hazardous condition: (1) Israel lacks a mandatory iodine fortification program [16,23], and only nine participants (only 4% of the total study population) reported voluntary consumption of iodized table salt; (2) despite Ministry of Health's guidelines recommending prenatal ICS use at least one month prior to conception, only 6% of the current study participants reported pre-pregnancy initiation of ICS intake. Moreover, the estimated iodine from ICS was 62 µg/day, although the current study participants reported that the majority of ICS they consumed contained 220 µg of iodine per tablet.…”

Does Iodine Intake Modify the Effect of Maternal Dysglycemia on Birth Weight in Mild-to-Moderate Iodine-Deficient Populations? A Mother–Newborn Prospective Cohort Study

“…This study was a longitudinal prospective cohort study; its methods have previously been described in detail [ 16 ]. In brief, the study was conducted during the period of June 2018 to April 2020.…”

“…All in all, 202 pregnant women participated in the study. A detailed description of the screening procedure, study sample, and follow-up flow chart can be found elsewhere [ 16 ]. The BUMCA’s ethical committee approved the study (no’ 001-17-BRZ dated 7 August 2017).…”