The relationship between excessive iodine during pregnancy and adverse pregnancy complications

Iodine nutrition during pregnancy plays an important role in fetal development and maternal outcomes. Iodine deficiency has been proved to be associated with maternal thyroid dysfunction, adverse fetal outcomes and neurodevelopmental disorders in offspring. At present, there are few studies concentrate on the effects of iodine excess during pregnancy on thyroid function, maternal and neonatal outcomes, and the results are still controversial. The aim of this study was to evaluate the effects of excessive iodine status on thyroid function, glycolipid metabolism, and maternal and neonatal outcomes.

A total of 595 pregnant women who gave birth at the First Affiliated Hospital of Nanjing Medical University from January 2023 to December 2023 were included in this study. Blood and urine samples were collected during the second trimester of pregnancy. Thyroid function include thyroid-stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3) and urinary iodine concentrations (UIC) were measured. Maternal and neonatal outcomes were collected.

Participants were divided into four groups based on UIC, with median UIC values of 100.5, 200, 314.2, and 655 μg/L, respectively. UIC was found to be positively associated with TSH, and negatively associated with FT3 and FT4. Fasting blood glucose (FBG) levels were elevated both in iodine deficiency and excess group. A U-shaped relationship between UIC and thyroid dysfunction were found. Iodine deficiency, excess iodine and even more than adequate iodine can lead to increased incidence of thyroid diseases such as isolated hypothyroxinaemia and overt hyperthyroidism. Importantly, iodine excess was found to be related with higher prevalence of umbilical cord around neck and eclampsia as well as higher blood glucose and low-density lipoprotein(LDL) level.

Abnormal iodine status especially iodine excess during pregnancy was found to be related with higher prevalence of adverse mother and fetus outcomes, abnormal blood glucose and lipid level.