Iodine nutritional status in different trimesters of pregnancy and its association with dietary habits: a prospective observational study in Taiwan

Abstract

Background: Pregnant women are susceptible to iodine deficiency. Most iodine nutritional studies in pregnant women have involved cross-sectional evaluations of iodine status. This prospective observational study was designed to longitudinally follow the iodine status of pregnant women in different trimesters of pregnancy and to assess the demographic characteristics and dietary influences on iodine status.

Methods: A prospective cohort study was conducted at Taipei Veterans General Hospital from March 2019 to July 2022. A total of 211 women were enrolled and each subject was asked to provide a spot urine sample at each trimester. Urinary iodine concentration (UIC) was measured using inductively coupled plasma-mass spectrometry. Dietary habit was assessed via food frequency questionnaires (FFQs) at each trimester.

Results: The median UICs for the first, second and third trimesters were 156.3 µg/L (interquartile range [IQR]: 100.7-241.1), 146.2 µg/L (84.6-224.4), and 169.9 µg/L (94.4-283.5), respectively. Compared to the first trimester, participants consumed seaweed (p = 0.004 and p < 0.001, respectively), fish (p < 0.001 for both), and prenatal multivitamins (p < 0.001 for both) more frequently during the second and third trimesters. Additionally, an increasing number of women raised their intake of dairy products as their pregnancies progressed. Multivariate analysis indicated a positive association between nulliparity and UIC < 150 µg/L (adjusted odds ratio [OR]: 2.258, 95% confidence interval [CI]: 1.167-4.367, p = 0.02). Additionally, less prenatal iodine-containing multivitamin intake increased the odds of UIC < 150 µg/L across all trimesters (adjusted OR: 2.562, 95% CI: 1.234-5.319; p = 0.01 for the first trimester; adjusted OR: 2.264, 95% CI: 1.167-4.395; p = 0.02 for the second trimester; and adjusted OR: 2.022, 95% CI: 1.031-3.967; p = 0.04 for the third trimester).

Conclusions: Mild iodine deficiency was observed in the second trimester despite adequate iodine status in the first and third trimesters. Nulliparous women and those not ingesting iodine-containing multivitamins are at greater risk of iodine deficiency, highlighting the need for targeted dietary education and interventions.

Keywords: Diet; Gestation; Iodine; Pregnancy; Taiwan.