FIG. 5.

Timing of initiation of iodine-containing supplements in pregnancy and measures of maternal thyroid function, adjusted models. Timing was categorized as: no reported supplement use (never; n = 1738), first use in weeks 1–26 before conception (preconception; n = 347), first use during first trimester (GW 0–12; n = 323), and first use during second trimester (GW 13–20; n = 194). Participants who reported use of iodine-containing supplements in the FFQ but did not report timing of use (n = 308) were not included in this analysis. For TSH, the geometric mean was modelled (by square root transformation), and for FT3 and FT4 the highest first percentile was excluded to obtain ∼normal distribution. Crude models are included in Supplementary Fig. S10, and models excluding antibody positive women in Supplementary Fig. S9. *p < 0.05. GW, gestational week.