Physician-scientists from the neuroendocrine unit at Mass General Boston evaluated thyroid function measurements in health records of 239 women undergoing infertility evaluations over 13 years.
Infertility is defined by inability to get pregnant after one year of unprotected intercourse and occur in 7-15% of women in the US, The cause of infertility is usually found in the majority of couples. Causes in women stem from age, abnormal ovulation, anatomic issues in the tubes or uterus, and hormonal derangements including insulin resistance, hypo and hyperthyroidism. Male factors for infertility involve issues with low numbers and quality (low motility and form) of sperm. In 10-30% of couples the cause of infertility is unknown or unexplained: Unexplained infertility. These couples are “normal” by all criteria including having thyroid tests (TSH) within the normal range of the assay (TSH within the range of 0.4 to 5 mIU/L) and no history of autoimmune (+ TPO-AB) thyroid disease.
The investigators wondered if there would be differences, within the TSH normal range, in 187 women with unexplained infertility versus 52 women whose infertility was due to their partner (male factor). Significantly they found that 26.9% of women with unexplained infertility had TSH greater than 2.5 mIU/L compared to only 13.% in women with male factor infertility. Data remained the same (26% versus 12%) when they removed from the analysis 3 women from each group who also had elevated thyroid antibodies (TPO-AB) or Hashimotos. Unfortunately we do not know if lowering the TSH value to equal or less than 2.5 mIU/L would have led to a shorter time to conception. More research is needed!
The data supports the idea that mild abnormalities in thyroid function may contribute to some cases of unexplained infertility, and it may not be unreasonable to give a trial of thyroid hormone to bring TSH under 2.5 mIU/L before embarking on a more expensive and resource intensive in vitro fertilization treatment. To date there is no indications for thyroid hormone replacement in women whose TSH is in the current normal range 0.4-4.0 mIU/L, unless they have both a +TPO-AB and are seeking fertility treatment, or if a woman has +TPO and her TSH is in the 4-10 range to prevent miscarriage.
Tehereh Orouji Jokar etal. February 2018’s Journal of Clinical Endocrinology and Metabolism 103(2);632-639.