Underachieving thyroid within the normal range associated with unexplained infertility

Even a mildly dysfunctional thyroid can impair a woman’s ability to conceive – and this is true even when the thyroid’s ability is within what is currently considered the normal range. A thyroid gland functioning at the low end of the normal range can thus pose a problem when a woman wishes to become pregnant.

These new findings, published in the Endocrine Society’s Journal of Clinical Endocrinology & Metabolism, may help explain previously unexplained instances of infertility in women.

Higher levels of TSH linked to infertility

In a study led by Pouneh K. Fazeli (M.D., M.P.H., of Massachusetts General Hospital and Harvard Medical School in Boston), women diagnosed with unexplained infertility were show to be nearly twice as likely* to have higher levels of a thyroid-stimulating hormone (TSH) produced by the pituitary gland. Elevated levels of TSH can be a sign that the thyroid gland is underperforming and that they pituitary gland is trying to prompt the thyroid to produce more hormones.

In the study, women with unexplained infertility were nearly twice as likely to have a TSH value greater than 2.5 mlU/L compared to women where the infertility was due to known issues with their male partner’s fertility.

“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,” says Fazeli. “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.”  […] “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.”

What is unexplained fertility?

For this study, unexplained fertility was defined as the inability to conceive within 12 months of unprotected intercourse and where a medical evaluation shows no reason for the infertility.

Who was in the study?

The study included female patients between the ages 18-39 years who had been diagnosed with infertility at Partners HealthCare System hospitals in Boston, Massachusetts, USA between 2000 and 2012.

Only women with regular menstrual cycles and normal fertility evaluation were included in the study.

The researchers had access to TSH levels from 187 women with unexplained infertility and 52 TSH levels from women whose partners had been diagnosed with severe infertility.

Read more

Higher TSH levels within the normal range are associated with unexplained infertility.

The Journal of Clinical Endocrinology & Metabolism, 2017
DOI: 10.1210/jc.2017-02120


Tahereh Orouji Jokar
Lindsay T Fourman
Hang Lee
Katherine Mentzinger
Pouneh K Fazeli