Hysterosalpingography (HSG) with oil-soluble contrast medium (OSCM) improves pregnancy rates in infertile women by unclear mechanisms1, 2. OSCM has a high iodine content and long half-life with a potential to cause iodine excess post-HSG3. As a secondary outcome of a study examining the impact of this iodine load (SELFI study)4, we determined factors associated with improved pregnancy rates following an OSCM HSG.
196 consecutive consenting infertile women undergoing OSCM HSG were recruited (Auckland, 2019-2021). Baseline levels and serial measurements of urine iodine concentration (UIC), thyroid function tests and anti-mullerian hormone (AMH) were performed for 6 months post-procedure. Pregnancy and treatment with levothyroxine during the study period were documented.
Median age of the cohort was 36 years (26-49 years). Pregnancy rates were high in women under 40 years with a steep decline in rates in women ≥ 40 years (51% in < 35 years, 47% in 35–39 years and 16% in ≥40 years). A higher AMH was associated with greater chance of pregnancy. 29% participants were iodine deficient at baseline, while 55% iodine sufficient, and 16% had iodine excess. A lower UIC at baseline was associated with a greater likelihood of pregnancy following the HSG. Women who became pregnant had baseline UIC 21% lower than those who did not become pregnant (95% CI -38%, -1%; p=0.042). Among participants with subclinical hypothyroidism(n=79) following HSG, there was a trend for those treated with levothyroxine to get pregnant compared to those not treated and this result was significant when only women under 40 years were considered (63% vs 37%; p=0.047).
In conclusion, OSCM HSG improved pregnancy rates, but was less useful in women aged ≥40 years. Iodine deficiency was relatively common in this cohort and increased iodine levels from OSCM exposure may contribute to the improved fertility observed with this procedure.