Is thyroid disease associated with infertility in women?

Thyroid Disease and Female Infertility

Yes, thyroid disease is definitively associated with infertility in women and should be evaluated as part of the basic infertility workup. Both hypothyroidism and hyperthyroidism can impair fertility through direct effects on ovulation, menstrual regularity, and reproductive hormone balance 1.

Why Thyroid Disease Causes Infertility

Thyroid disorders are recognized as medical conditions associated with reproductive failure and must be included in the infertility evaluation 1. The mechanisms include:

• Anovulatory cycles and menstrual irregularities: Both hypo- and hyperthyroidism disrupt normal ovulatory function 2, 3
• Elevated prolactin levels: Hypothyroidism increases thyrotropin-releasing hormone (TRH), which stimulates prolactin secretion, leading to hyperprolactinemia and infertility 2
• Sex hormone imbalances: Thyroid dysfunction affects the hypothalamic-pituitary-ovarian axis 4, 3

Clinical Approach to Screening

All women presenting with infertility should be screened for thyroid disease as part of the initial evaluation 1. The workup should include:

• Medical history focusing on: symptoms of thyroid disease (fatigue, weight changes, heat/cold intolerance, menstrual irregularities), history of thyroid disorders, and family history of reproductive failure 1
• Physical examination including: thyroid palpation for enlargement, nodules, or tenderness; assessment for signs of hypo- or hyperthyroidism 1
• Laboratory testing: TSH as initial screening test, with free T4 or free thyroxine index if TSH is abnormal 1

Treatment Thresholds and Goals

Women with TSH >4.0 mIU/L should be treated with levothyroxine, as this improves fertilization rates, embryo quality, and live birth rates 4. For women planning assisted reproductive technology:

• Target TSH <2.5 mIU/L before conception or ART 4, 5
• Women already on levothyroxine typically require 30% or more dose increase by 4-6 weeks gestation 1
• Monitor thyroid function every 2-4 weeks during early pregnancy 1, 6

Special Considerations

Thyroid autoimmunity (positive anti-thyroid antibodies) is more prevalent in women with ovarian and unexplained infertility 4, 3. Key points:

• Higher TPO antibody titers increase miscarriage risk even when TSH is controlled with treatment 7
• Controlled ovarian hyperstimulation during ART can strain thyroid function, particularly in women with thyroid autoimmunity 4, 3
• For euthyroid women with thyroid autoimmunity, levothyroxine should be considered on a case-by-case basis if TSH >2.5 mIU/L 4

Hyperthyroidism and Fertility

Untreated hyperthyroidism increases risk of miscarriage and should be controlled before attempting pregnancy 1. Guidelines recommend:

• Achieve euthyroidism before conception 1
• Propylthiouracil is preferred in first trimester; methimazole in second and third trimesters 1, 6
• Radioactive iodine is contraindicated and may have gonadal toxicity affecting ovarian reserve 5

Common Pitfalls

Fertility problems may persist even after restoring normal thyroid function, requiring additional fertility interventions 4. Do not assume thyroid treatment alone will resolve infertility—concurrent evaluation of both partners should proceed 1. Additionally, subclinical hypothyroidism and thyroid autoimmunity can remain asymptomatic and undiagnosed, making routine screening essential in the infertility workup 3.