Does perimenopause increase abnormal uterine bleeding and risk of iron deficiency?

The transition into perimenopause involves significant physiological shifts that directly impact uterine health and systemic iron stores. Research confirms that the hormonal instability characteristic of this stage is a primary driver of both irregular bleeding patterns and subsequent iron depletion.

Clinical and mechanistic evidence

The relationship between perimenopause, bleeding patterns, and iron status is well-documented through clinical and mechanistic findings:

• Anovulatory Mechanisms: During perimenopause, declining ovarian reserves lead to inconsistent follicle-stimulating hormone (FSH) surges, causing approximately 20% of cycles to be anovulatory. In these cycles, the corpus luteum fails to form, resulting in a progesterone deficiency. This creates a state of unopposed estrogen, where the endometrium continues to proliferate without the structural stabilization provided by progesterone.
• Pathophysiology of Bleeding: This hormonal imbalance often leads to endometrial hyperplasia and increased tissue fragility. Clinically, this is categorized as AUB-O (ovulatory dysfunction) under the FIGO PALM-COEIN framework. This manifests as heavy menstrual bleeding (menorrhagia) or unpredictable, prolonged cycles.
• Impact on Iron Stores: Heavy menstrual bleeding (HMB) is a leading cause of iron deficiency (ID) and iron deficiency anemia (IDA) in midlife. Because each milliliter of blood contains approximately 0.5 mg of iron, chronic excessive loss quickly exceeds dietary intake and the body's absorption capacity.
• Diagnostic Markers: Clinical guidelines suggest that serum ferritin levels below 30–50 μg/L are diagnostic of iron depletion in this population. Research indicates that HMB affects 30–50% of reproductive-age and perimenopausal women, accounting for a significant portion of iron deficiency cases globally.

Clinical implications

For women in midlife, managing abnormal bleeding is critical not only for quality of life but for maintaining hematological health. Because non-anemic iron deficiency (NAID) can occur before hemoglobin levels drop, clinicians often recommend screening both hemoglobin and ferritin in patients experiencing perimenopausal cycle changes.

Bottom line

Perimenopause increases the frequency of anovulatory cycles, leading to unopposed estrogen and abnormal uterine bleeding. This excessive blood loss is a medically recognized and common cause of iron deficiency in midlife women, requiring proactive monitoring of iron stores and cycle management.