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Mild thyroid dysfunction may lead to unexplained infertility

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December 19, 2017

Women with unexplained infertility are nearly twice as likely to have high-normal thyroid-stimulating hormone 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.

“When couples who are ready to start a family are unable to conceive despite extensive planning, multiple doctor’s visits and expensive treatments, it can be emotionally devastating,” Pouneh K. Fazeli, MD, MPH, of Massachusetts General Hospital and Harvard Medical School, said in a press release. “Since our study shows that women with unexplained infertility have higher TSH levels compared to women experiencing infertility due to a known cause, more research is needed to determine whether treating these higher TSH levels with thyroid hormone can improve their chances of getting pregnant.”
In a cross-sectional study, Fazeli and colleagues 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) who received care at Partners Health Care System between 2000 and 2012. 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; P = .003), 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%; P < .05). There were no between-group differences for prolactin levels.

“Since we now know from our study that there is an association between TSH levels at the high end of the normal range and unexplained infertility, it is possible that a high-normal TSH level may negatively impact women who are trying to get pregnant,” Fazeli said in the release. “This could open up new avenues for possible treatments. The next step will be to see if lowering TSH levels will help this group conceive.” – by Regina Schaffer

Disclosures: The authors report no relevant financial disclosures.

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