# Mild-to-moderate iodine deficiency among pregnant women in Ireland: data from a large prospective pregnancy cohort

## TL;DR

This study found that pregnant women in Ireland have mild-to-moderate iodine deficiency, which is important for fetal brain development.

## Contribution

This is the first large-scale assessment of maternal iodine status in Ireland.

## Key findings

- Median urinary iodine concentrations indicated mild-to-moderate iodine deficiency during pregnancy.
- Iodine-containing supplement use, winter season, BMI, age, and education predicted lower iodine-to-creatinine ratios.

## Abstract

Adequate maternal iodine status is essential for healthy foetal brain development. There are no current data on maternal iodine status in Ireland. The aim of this study was to conduct the first large-scale assessment of maternal iodine status in Ireland and identify its sociodemographic determinants using data from a large prospective pregnancy cohort.

Participants were nulliparous females (n = 1509) recruited at Cork University Maternity Hospital, Cork, Ireland. Clinical and questionnaire-based assessments were carried out and spot urine samples were collected throughout pregnancy. Urinary iodine concentration (UIC) at 11 and 15 weeks of gestation was quantified using the Sandell–Kolthoff colorimetric method. UIC was corrected for urinary creatinine (measured via Jaffe assay), expressed as I: Cr ratio. Linear and logistic regression were performed to identify non-dietary determinants of iodine status in early pregnancy.

Median (IQR) UIC at 11 and 15 weeks of gestation were 128 (76, 201) and 125 (74, 208) µg/L, respectively, indicating mild-to-moderate iodine deficiency during pregnancy at both timepoints. Iodine-containing supplement use, winter season, BMI, age and education were predictors of I: Cr < 150 µg/g.

This first large-scale investigation of maternal iodine status in Ireland highlighted sub-optimal status in pregnancy.

The online version contains supplementary material available at 10.1007/s00394-025-03692-z.