Stage-specific variations in urinary and salt iodine among pregnant women in Beijing

Background Iodine is essential for fetal neural development and thyroid function in pregnant women. Although China has a policy of iodizing salt, salt intake alone may be insufficient to fulfill the iodine needs of pregnant women, particularly in early gestation. Purpose To evaluate trimester-specific and annual fluctuations in urine and salt iodine levels among pregnant women in Beijing from 2021 to 2024. Methods Iodine data from 400 women were analyzed using descriptive statistics, ANOVA and MEM. Results The median urinary iodine decreased from 151.3 μg/L in 2022 to 122.9 μg/L in 2024, falling outside the WHO recommended threshold of 150 μg/L. ANOVA indicated a substantially reduced urine iodine level in the first trimester compared to subsequent trimesters ( F = 4.72, P = 0.011). MEM showed reduced levels in the first trimester (β = –0.34, P = 0.01), whereas salt iodine shown no variations across trimesters (β = 0.45, P = 0.80). The iodine content in salt remained consistent (19–22 mg/kg), however urine iodine decreased by 17%–24% over time. Conclusion Urinary iodine levels among Beijing pregnant women have declined significantly, particularly in early pregnancy. Iodized salt alone is insufficient to meet their needs, therefore enhanced iodine supplementation and early monitoring are crucial to ensuring sufficient iodine intake for embryonic development.