For many years I have been routinely testing new patients’ thyroid function because the recommendation for women trying to conceive is a thyroid stimulating hormone (TSH) level of less than 2.5. The cutoff for the normal range is usually greater than 2.5 and may vary between various doctor’s and lab’s recommendations.
Women with unexplained infertility are nearly twice as likely to have high-normal thyroid-stimulating hormone (TSH) levels compared with women with a normal fertility evaluation, according to findings published in The Journal of Clinical Endocrinology & Metabolism. The finding suggests that even mild variations in thyroid dysfunction within the normal range may be an important factor in fertility, according to the researchers.
They analyzed electronic records data from 187 women who did not conceive after at least 1 year with appropriate exposure to sperm (unexplained infertility; mean age, 31 years; median BMI, 23 kg/m²) and 52 women who did not conceive after 1 year who had inadequate exposure to sperm due to a male partner with azoospermia or severe oligospermia (severe male factor infertility; mean age, 30 years; median BMI, 24.4 kg/m²). All participants had a TSH measurement within the “normal” range of the assay (TSH 5 mIU/L). Women with a history of hypothyroidism, hyperthyroidism, high prolactin level or recurrent miscarriage were excluded.
Researchers found that median TSH levels were greater in the unexplained infertility group vs. controls (mean, 1.95 mIU/L vs. 1.66 mIU/l), with results persisting after adjusting for BMI, age and smoking status. Additionally, nearly twice as many patients in the unexplained infertility group had a TSH level of at least 2.5 mIU/L vs. controls (26.9% vs. 13.5%). The authors concluded, ” The next step will be to see if lowering TSH levels will help this group conceive.”
I believe a future study will show that it will improve pregnancy rates and so I have been treating patients with TSH levels over 2.5 to bring them lower.