Assessment of Iodine Status Among Pregnant Women in Sri Lanka Using Urinary Iodine Concentration.

Technical Summary: Assessment of Iodine Status Among Pregnant Women in Sri Lanka

Problem Statement
Despite the implementation of Universal Salt Iodisation (USI) in Sri Lanka since 1995, which successfully reduced iodine deficiency disorders (IDDs) at the general population level, emerging evidence suggests persistent gaps in iodine status specifically among pregnant women. Iodine is critical for maternal thyroid hormone synthesis and fetal neurodevelopment; even mild deficiency during pregnancy is linked to adverse cognitive outcomes in offspring. Previous national surveys (2012–2016) indicated that a significant proportion of pregnant women remained iodine insufficient, with median urinary iodine concentrations (mUIC) falling below the World Health Organization (WHO) recommended threshold. This study addresses the need for updated, pregnancy-specific data to evaluate whether current USI programs adequately meet the heightened physiological demands of pregnancy.

Methodology
The research employed a cross-sectional design involving 337 first-trimester pregnant women attending antenatal clinics (ANCs) across three purposively selected districts representing distinct ecological zones in Sri Lanka:

• Colombo: Wet zone (Western Province)
• Kandy: Intermediate zone/Hill country (Central Province)
• Anuradhapura: Dry zone (North Central Province)

The study utilized a stratified sampling approach to capture urban and rural variations, targeting 65 participants per setting within each district. Spot urine samples were collected in sterile containers, transported at 4°C, and stored at -20°C. Urinary Iodine Concentration (UIC) was measured using the ammonium persulphate-modified microplate method. Quality control was rigorous, involving internal validation with known samples and external validation through the US CDC EQUIP program.

Statistical analysis was conducted using IBM SPSS v26. UIC values were categorized according to WHO criteria for pregnant women:

• Insufficient: <150 µg/L
• Adequate: 150–249 µg/L
• Above requirements: 250–499 µg/L
• Excessive: ≥500 µg/L

Differences between districts were assessed using the Kruskal–Wallis test, with pairwise comparisons performed using the Mann–Whitney U test with Bonferroni correction.

Key Results

• Overall Status: The overall median UIC (mUIC) for the study population was 135.9 µg/L, which falls below the WHO-recommended range of 150–249 µg/L for pregnancy. The data distribution was positively skewed, indicating a substantial proportion of women with low iodine levels.
• Deficiency Prevalence: 52.8% of participants were classified as iodine insufficient (<150 µg/L). Only 22.6% fell within the adequate range.
• Excess Intake: A notable minority exhibited higher-than-required levels: 20.8% were "above requirements" (250–499 µg/L) and 3.9% had "excessive" levels (≥500 µg/L).
• Geographic Disparities: Significant variation was observed across districts (p=0.004):
  • Colombo (Wet Zone): Highest mUIC at 168.1 µg/L. This district also had the highest prevalence of excess intake (8.0% excessive, 26.0% above requirements).
  • Kandy (Intermediate Zone): Lowest mUIC at 106.4 µg/L, indicating the most severe deficiency.
  • Anuradhapura (Dry Zone): mUIC of 131.9 µg/L.
  • Post-hoc analysis confirmed that Colombo had significantly higher UIC values than Kandy (p=0.003).
• Urban-Rural Differences: While urban participants generally showed higher mUIC values than rural participants, the difference was not statistically significant (p>0.05). However, specific district-level trends varied; for instance, in Anuradhapura, rural women had higher UIC than urban women.

Key Contributions

1. Updated Surveillance: The study provides the most recent assessment of iodine status among Sri Lankan pregnant women, highlighting that population-level sufficiency (achieved via USI) does not guarantee adequacy for this high-risk group.
2. Identification of Dual Burden: The research documents a coexistence of iodine insufficiency and excess intake within the same population. While over half the sample was deficient, nearly a quarter had intakes above requirements, with a small but significant group at risk of excessive intake.
3. Geographic Granularity: By stratifying data across ecological zones, the study reveals that iodine status is not uniform across Sri Lanka. The "wet zone" (Colombo) shows different patterns compared to the "hill country" (Kandy) and "dry zone" (Anuradhapura), suggesting that national averages may obscure local vulnerabilities.

Significance and Claims
The authors conclude that nearly three decades after the introduction of USI, iodine insufficiency persists among pregnant women in Sri Lanka, characterized by wide district-level disparities and emerging pockets of excessive intake.

The paper claims that these findings necessitate a shift in public health strategy from broad population monitoring to strengthened, pregnancy-specific monitoring. The authors argue that the current USI program requires periodic evaluation and potential adjustment to address:

• The specific physiological demands of pregnancy.
• Geographic and sectoral variations in iodine intake.
• The risk of both deficiency and excess.

The study advocates for improved regulatory enforcement of salt iodisation standards, better household availability of adequately iodized salt, and the promotion of appropriate prenatal iodine supplementation to safeguard maternal thyroid health and optimize fetal neurodevelopment. The authors emphasize that without targeted interventions, the progress made in eliminating iodine deficiency disorders may be compromised for future generations.