New research suggests that even a mildly underactive thyroid could affect a woman’s ability to get pregnant—even when thyroid hormone levels are technically in the normal range. The findings were published in the Journal of Clinical Endocrinology & Metabolism, a journal of the Endocrine Society.
The study showed that women with unexplained infertility were almost twice as likely to have higher levels of thyroid-stimulating hormone (TSH) compared to women whose infertility was due to a known cause, such as poor sperm quality in their partners. TSH is produced by the pituitary gland in the brain and signals the thyroid to release hormones. When TSH levels are high, it can indicate the thyroid is underactive.
Unexplained infertility refers to cases where couples cannot conceive despite trying for months, and no clear medical cause is found. According to the U.S. Department of Health and Human Services, about 10% of American women between 15 and 44 years old struggle to get or stay pregnant. Of these cases, between 10% and 30% are classified as unexplained.
Dr. Pouneh K. Fazeli, senior author of the study and a physician at Massachusetts General Hospital and Harvard Medical School, highlighted the emotional impact of unexplained infertility. “Couples go through a lot—doctor visits, treatments, and emotional stress. Our research found that women with unexplained infertility had higher TSH levels than those whose infertility had a known cause,” she said. “This raises the question of whether treating high-normal TSH levels could improve fertility outcomes.”
The study analyzed records from women aged 18 to 39 who were treated for infertility between 2000 and 2012 at hospitals in the Partners HealthCare System in Boston. The researchers only included women with regular menstrual cycles and no identified fertility problems. They compared TSH levels from 187 women with unexplained infertility to 52 women whose partners had severe male infertility.
Results showed that women with unexplained infertility had significantly higher TSH levels. Nearly twice as many in this group had TSH levels above 2.5, compared to the group whose partners had fertility issues.
Dr. Fazeli emphasized that this connection could lead to new treatment options. “Now that we see a link between high-normal TSH levels and unexplained infertility, the next step is to explore whether lowering those TSH levels can help these women conceive,” she said.
Related topics:
