Endocrine Abstracts

Background and Objectives: During pregnancy normal thyroid activity undergoes significant changes, including an increase in the amount of iodine intake and maternal renal iodine excretion. Hence, dietary iodine requirements are higher in pregnant women than in non-pregnant ones. This study aimed to assess the nutritional iodine status in a large group of pregnant women and thyroid function according to different iodine intake and thyroid diseases.

Methods: A total of 1413 consecutive nonselected pregnant women were enrolled from 2012 to 2021 in the Endocrinology Unit of Pisa Hospital; 519 (36.7%) had no thyroid diseases (control group), 580 (41%) were diagnosed with autoimmune thyroiditis (AT), 66 (4.7%) with Graves disease (GD), 181 (12.8%) with nodular thyroid diseases (ND) and 67 (4,8 %) were affected by other thyroid disorders. We collected data about the use of iodized salt and/or a dietary supplement containing iodine and we measured urinary iodine concentration (UIC) in a single urine spot with mass spectrometry in each trimester of gestation. We defined the following categories of UIC in pregnancy: iodine deficiency if UIC was under 150 mg/l and adequate iodine intake if UIC was over 150 mg/l.

Results: The iodine status of our population is described in Table 1. During the first trimester, 20% of women did not assume any iodine supplementation (N), 29% utilized iodized salt (S), 19.9 % multivitamins containing iodine (M), and 30.8% both (B). Median UIC was 68, 73, 103, and 148 mg/l in groups N, S, M, and B, respectively, with statistically significant difference between group M and N (P = 0.039), group B and M (P = 0.001), B and S (P = 0.000), B and N (P = 0.000). These results were independent of thyroid diseases. In addition, we evaluated thyroid function according to iodine intake, excluding women under medication with L-thyroxine. When iodine deficiency was present, TSH concentration was significantly higher in AT women than in the control group in the first (P = 0,000), second (P = 0,000), and third (P = 0,008) trimesters of gestation. No differences were found when iodine intake was adequate.

Conclusions: Only women who assumed both iodized salt and multivitamins containing iodine reached the recommended iodine urinary levels in pregnancy. In AT women iodine deficiency was associated with a worse thyroid function than in the control group, thus confirming the importance of an iodine dietary supplementation from early pregnancy.