Thyroid

Thyroid is a small, butterfly-shaped gland at the front of the neck. It produces the hormones thyroxine (T4) and triiodothyronine (T3). It also produces calcitonin. These hormones set the rate at which the body uses energy. They also help regulate growth, body temperature, and calcium in the blood.

When the thyroid produces too much or too little hormone, the cycle can change. Periods can become irregular. Ovulation can stop. The luteal phase, the second half of the cycle, can fall short. Thyroid disorders are associated with infertility, miscarriage, and preterm birth.¹ Thyroid disorders in men can also affect sperm.¹ Common diagnoses include an underactive thyroid (hypothyroidism) and an overactive thyroid (hyperthyroidism). A milder underactive form (subclinical hypothyroidism) is also common. In some women, the immune system attacks the gland (autoimmune thyroiditis). Blood tests then show thyroid peroxidase (TPO) or thyroglobulin (Tg) antibodies.

Restorative Reproductive Medicine seeks the underlying cause of infertility and recurrent pregnancy loss. The thyroid is often part of that search. Practice varies from clinician to clinician. Many RRM clinicians measure thyroid-stimulating hormone (TSH) and free T4. Some also measure TPO and Tg antibodies. Some add free T3 or reverse T3 when early results do not agree. Many aim for a narrower TSH range when a couple is trying to conceive. NaProTechnology evaluation considers thyroid care as part of the whole fertility picture, alongside support for ovulation.

One large trial gave thyroid hormone to women with thyroid antibodies but normal thyroid levels. The treatment did not increase live births.² That trial tested one drug in women selected by one laboratory marker. Other causes of infertility in the couple were outside its scope.

Thyroid cancer is a separate disease of the gland itself. It is outside the scope of fertility hormone testing.