Maternal Serum Iodine Concentrations in Early Pregnancy Exhibited Well Diagnostic Ability for Thyroid Dysfunction, Inverse Associations with Gestational Weight Gain, and Birth Size: Longitudinal Analyses Based on Huizhou Mother-Infant Cohort.

The study aims to explore the associations of maternal serum iodine concentrations (SIC) with thyroid function, obstetric, and birth outcomes. This was a prospective study embedded in the Huizhou Mother-Infant Cohort. Singleton mothers aged 18-45 years were enrolled at their first antenatal visits. Maternal SIC and thyroid markers were tested by inductively coupled plasma mass spectrometry and electronic chemiluminescent assay, respectively. Obstetric and birth outcomes were retrieved from the Hospital Information System. Two nested 1:1 age and body mass index-matched case-control studies were embedded in the cohort including 224 pairs of mothers with gestational diabetes mellitus (GDM) and 302 paired of newborns with small for gestational age (SGA) and their respective healthy controls. Multivariable linear and conditional logistic regression models were applied to explore the relationship of maternal SIC with obstetric complications and birth outcomes. A total of 1558 mothers were included for analysis. Receiver operating characteristic curve (ROC) analysis showed that maternal SIC in the 1st trimester (T1) had well diagnostic ability for clinical and subclinical hyperthyroidism, clinical hypothyroidism, and hypothyroxinemia with the areas under the curve of 0.907, 0.734, 0.867, and 0.927, respectively (all p < 0.05). Mothers in the highest quartile of SIC at T1 had an increased risk of SGA (OR = 2.043, 95% CI: 1.198-3.483, p = 0.009) but not for GDM risk. Maternal SIC were significantly and inversely associated with gestational weight gain (GWG), birth weight, and Ponderal index (all p < 0.05). SIC at T1 had well diagnostic values for thyroid dysfunction. High gestational SIC during early pregnancy were associated with lowered GWG, birth size, and increased risk of SGA. Study registration no: NCT03922087 at Clinicaltrial.gov.com.