Thyroid Disorders and Abnormal Uterine Bleeding
Yes, thyroid disorders are a well-established cause of abnormal uterine bleeding (AUB), with hypothyroidism being the most common thyroid dysfunction associated with this condition.
Prevalence and Association
Thyroid dysfunction is a significant contributor to AUB cases, with studies demonstrating substantial prevalence rates:
- Approximately 48% of patients with AUB have deranged thyroid profiles, with hypothyroidism accounting for 91.6% of these thyroid abnormalities 1
- Subclinical hypothyroidism occurs in approximately 33% of perimenopausal women presenting with AUB 2
- Overall thyroid dysfunction prevalence ranges from 13.9-15.8% in AUB patients, with hypothyroidism being the predominant type (60-100% of thyroid dysfunction cases) 3, 4
Mechanism and Clinical Patterns
Thyroid hormones profoundly affect the female reproductive system through multiple pathways:
- Both hypothyroidism and hyperthyroidism cause anovulatory cycles, delayed puberty onset, and reproductive dysfunction 3
- Hypothyroidism is frequently associated with increased endometrial thickness, which contributes to abnormal bleeding patterns 1
- The most common bleeding pattern in thyroid dysfunction is menorrhagia (heavy menstrual bleeding), followed by polymenorrhea and oligomenorrhea 3
Clinical Implications and Screening
Thyroid function tests (TFTs) should be performed as part of the initial evaluation of AUB, as they are an effective and economical means of identifying underlying causes 1:
- This is particularly important in women 35 years or older with recurrent anovulation 5
- Body mass index correlates significantly with subclinical hypothyroidism in AUB patients (p=0.03) 2
- Oligomenorrhea rates are significantly higher in patients with subclinical hypothyroidism (p=0.05) 2
Treatment Considerations
Once thyroid dysfunction is identified:
- Treatment with combination oral contraceptives or progestins may regulate menstrual cycles in anovulatory bleeding 5
- The levonorgestrel-releasing intrauterine system is effective for menorrhagia management 5
- Addressing the underlying thyroid dysfunction is essential, as chronic anovulation from untreated thyroid disease leads to prolonged unopposed estrogen stimulation and increased endometrial cancer risk 5
Important Caveats
While thyroid dysfunction is a significant cause, structural abnormalities remain the most common etiology:
- Structural causes (adenomyosis, leiomyomas, polyps) account for 81.3% of AUB cases 1
- Most women with AUB (84.2-84.8%) are actually euthyroid 3, 4
- Therefore, thyroid screening should be part of a comprehensive evaluation that includes endometrial assessment via transvaginal ultrasonography and, when indicated, endometrial biopsy 1, 5