Iodine status assessed by repeated UIC measurements

Repeated gestational maternal UIC/creatinine ratio (UICcr) measurements have not yet been studied in such large numbers. We will therefore first investigate the classification and determinant characteristics. We will study to what extent first trimester UICcr measurements (currently used in most clinical studies) correlate to second and third trimester UICcr measurements. Furthermore, we will investigate which maternal and pregnancy characteristics are determinants of UICcr levels, or of the gestational variation in UICcr levels by using (non)linear mixed models. Future analyses can then be adjusted and/or stratified accordingly. Subsequently, iodine status will be classified according to the number of (ab)normal samples. Three groups will be created:1) iodine sufficient: women in which all samples measured a UICcr of >150 µg/L; 2) borderline insufficient status: women in which one sample measured a UICcr of <150 µg/L, 3) iodine insufficient: women with all, or 2/3 samples with a UICcr of <150 µg/L. Sensitivity analyses will be performed in order to investigate UICcr variation in women with borderline iodine status (mean UICcr >150 µg/L vs. <150 µg/L) and to investigate possible severe iodine insufficiency (at least one sample UICcr < 50 µg/L).