Abnormal Uterine Bleeding

❍ At a glance

• Classify before investigating: heavy menstrual bleeding (HMB), intermenstrual (IMB), postcoital (PCB), or postmenopausal (PMB). IMB and PCB raise the probability of cervical pathology and require speculum examination and swabs regardless of the apparent underlying cause. PMB must always be investigated to exclude endometrial carcinoma - this applies even in women on MHT.
• Von Willebrand disease is present in approximately 13% of women with HMB and is frequently missed. Consider vWD screening (APTT, vWF antigen, factor VIII) in adolescents and women without a structural or hormonal cause identified, or with a personal or family bleeding history.
• The LNG-IUS (Mirena) reduces menstrual blood loss by 70-90% and is the most effective medical treatment for HMB.³ Offer it early in management, not as a last resort before referral.
• Postmenopausal bleeding: transvaginal ultrasound is first-line. Endometrial thickness less than 4 mm in a woman not on MHT has a high negative predictive value for endometrial cancer, but biopsy is required when thickness is 4 mm or greater, when bleeding recurs, or when clinical suspicion is high regardless of ultrasound findings.

❍ Classification and presentation

The FIGO PALM-COEIN system classifies AUB by cause: structural causes (Polyp, Adenomyosis, Leiomyoma, Malignancy/hyperplasia) and non-structural causes (Coagulopathy, Ovulatory dysfunction, Endometrial, Iatrogenic, Not yet classified). In primary care, the most commonly encountered causes are ovulatory dysfunction, adenomyosis, fibroids, polyps, and iatrogenic causes (hormonal contraception, anticoagulants, antipsychotics). Malignancy must always be excluded, particularly in women over 45 or with risk factors.¹

Heavy menstrual bleeding (HMB) is defined clinically as blood loss that interferes with physical, emotional, social, or material quality of life. Ferritin and FBC are more useful markers of the impact than subjective reporting alone. Women commonly underreport - or normalise - excessive loss. Intermenstrual and postcoital bleeding raise the probability of cervical pathology (ectropion, polyps, cervicitis, carcinoma), endometrial polyps, or submucosal fibroids - speculum examination is mandatory. Irregular cycles suggest ovulatory dysfunction: check TFT and prolactin as first-line investigations.

❍ Investigation and management

First-line investigations: FBC and ferritin (all HMB), TFT and prolactin (irregular cycles), vWD screen (adolescents or HMB without structural cause identified²), cervical smear and swabs if IMB/PCB, and transvaginal ultrasound as the primary imaging modality. TVS identifies fibroids, adenomyosis, polyps, and endometrial pathology. Endometrial biopsy (Pipelle) is indicated for women over 45 with AUB, any postmenopausal bleeding, women with endometrial cancer risk factors (obesity, PCOS, tamoxifen, unopposed oestrogen), or suspicious USS findings. Sensitivity for endometrial carcinoma approaches 90%.

Medical management of HMB: The LNG-IUS is first-line and most effective, reducing loss by 70-90%.³ Tranexamic acid (1 g three to four times daily during menstruation) reduces loss by approximately 50%.⁴ NSAIDs provide modest reduction with the added benefit of treating dysmenorrhoea. The COCP reduces loss by around 40-50% and regulates cycles. High-dose oral norethisterone (5 mg three times daily, days 5 to 26) is a short-term option where IUS is declined. Iron deficiency anaemia requires treatment alongside the underlying cause. Surgical options for women who have completed their family include endometrial ablation, hysteroscopic polypectomy or myomectomy, and hysterectomy.

Any vaginal bleeding 12 or more months after the final menstrual period requires investigation to exclude endometrial carcinoma, regardless of MHT use. Endometrial cancer is the most common gynaecological malignancy in New Zealand; early detection substantially improves outcomes.

❍ Referral criteria

Refer urgently to gynaecology for: postmenopausal bleeding, suspected endometrial or cervical malignancy, or endometrial biopsy showing hyperplasia with atypia or carcinoma. Refer semi-urgently for: HMB not responding to first- and second-line medical therapy; structural cause (fibroid, adenomyosis, polyp) causing significant symptoms or subfertility; endometrial hyperplasia without atypia requiring surveillance; and women who wish to discuss surgical options. Do not delay referral for PMB while awaiting a smear result - a normal smear does not exclude endometrial pathology.