Iodine has been identified as a potential factor influencing female fertility during the childbearing years. The American Thyroid Association recommends that women attempting to conceive take a supplement containing 150 µg of iodine. However, no clinical trials have specifically examined the necessity of iodine supplementation in women experiencing infertility. Furthermore, no information is available on the optimal dose and duration of iodine supplementation to increase the chances of successful treatment in this group of women. Therefore, this study aims to investigate the effects of iodine supplementation on fertility parameters in infertile women.

This double-blind randomized clinical trial will be conducted in infertility clinic on women with diminished ovarian reserve and undergoing in vitro fertilization (IVF) cycle treatment. According to the Bologna criteria, decreased ovarian reserve is defined as having 3 to 5 antral follicles and an anti-Müllerian hormone concentration ranging from 0.1 to 1.5 ng/ml. All women diagnosed with diminished ovarian reserve who meet the inclusion and exclusion criteria outlined in the general information section of the clinical trial and have provided written consent to participate will be examined. Following enrollment and baseline measurements, women will be randomly assigned to treatment groups-placebo and iodine supplement (150 µg/day of iodine)-in a 1:1 allocation ratio, using a random number table. In the intervention group, women will take 150 µg of iodine daily (one tablet per day, Tavan Institute, Tehran, Iran) for two months prior to starting the new IVF cycle. In the control group, participants will take a placebo tablet daily (containing white wheat flour, designed to match the size, shape, and color of the iodine tablet, Tavan Institute, Tehran, Iran) for the same duration before beginning the new IVF cycle. Women of two groups will be followed until the end of IVF cycle. Women in both groups will be monitored until the completion of the IVF cycle. Throughout the study, the following parameters will be assessed based on the timeline of the IVF cycle: the number of retrieved oocytes, the number of mature (MII) oocytes, the number of embryos, embryo quality, biochemical pregnancy, and clinical pregnancy.

Inclusion Criteria:

• Women with diminished ovarian reserve
• Willingness to participate
• Age range: 18 to 45 years
• Women with a menstrual cycle of 21 to 42 days
• Women who have not used any contraceptive methods in the past 12 months
• Women who have not had in sexual intercourse for more than 2 months

Exclusion Criteria:

• Unwillingness to participate
• Women with polycystic ovary syndrome or endometriosis
• Diagnosis of any thyroid disease
• Use of any medication that affects the thyroid function
• Use of dietary supplements containing iodine (excluding those considered in the present study)
• Use of iodine-containing disinfectants