The following is a summary of “The SELFI Study: Iodine Excess and Thyroid Dysfunction in Women Undergoing Oil-Soluble Contrast Hysterosalpingography” published in the December 2022 issue of Endocrinology & Metabolism by Mathews et al.

Pregnancy rates are increased by hysterosalpingography (HSG) with an oil-soluble contrast medium (OSCM). But OSCM has a high iodine concentration and a lengthy half-life, which may cause iodine overload. For a study, researchers sought to ascertain the pattern of iodine excess following OSCM HSG and how it affected thyroid function.

With 196 consecutive consenting suitable women who did not have overt hypothyroidism or hyperthyroidism, a prospective cohort study was done. All participants finished the trial with compliance rates over 95%. The participants had OSCM HSG (Auckland, 2019–2021) along with 24-week serial monitoring of thyrotropin (TSH), free thyroxine (FT4), and urine iodine concentration (UIC). The primary outcome was the occurrence of subclinical hypothyroidism (SCH), which was determined as a non-pregnant TSH higher than 4 mIU/L with normal FT4 (11–22 pmol/L) in individuals with baseline thyroid function that was normal.

Nearly all people (98%) had iodine excess (UIC≥300 g/L), with UIC often peaking after 4 weeks. There was a significant iodine excess; 90% and 17% of subjects, respectively, had UICs more than or equal to 1,000 μg/L and greater than 10,000 μg/L. With 67% of those having a UIC more than or equal to 1,000 μg/L for at least three months, iodine excess persisted. The majority (96%) of cases of SCH (TSH 4–10 mIU/L) were moderate, and 38% of cases of SCH developed by week 4 (75%). The current treatment recommendations were reached by three subjects (TSH > 10 mIU/L). Treatment with thyroxine for moderate SCH appeared to increase the likelihood of conception (P =.063). In 9 participants (5%), hyperthyroidism (TSH <0.3 mIU/L) was present.

An obvious and protracted iodine excess was produced by OSCM HSG. SCH commonly coexisted with sporadic late-onset hyperthyroidism. For six months after the procedure, routine thyroid function tests were required.

Reference: academic.oup.com/jcem/article/107/12/3252/6704756