In a 41-year-old woman with abnormal uterine bleeding who requests contraception, what is the most appropriate investigation before prescribing contraception?

Ultrasound (Answer C)

Transvaginal ultrasound is the most appropriate initial investigation before prescribing contraception in this 41-year-old woman with abnormal uterine bleeding, as it serves as the essential first-line imaging modality to identify structural causes of bleeding and guide subsequent management decisions. 1, 2

Rationale for Ultrasound as the Initial Investigation

Primary Diagnostic Role

• Transvaginal ultrasound (TVUS) combined with transabdominal imaging is the recommended first-line diagnostic test for evaluating abnormal uterine bleeding in premenopausal women, providing comprehensive assessment of structural abnormalities such as polyps, adenomyosis, leiomyomas, hyperplasia, and malignancy. 1, 3

• TVUS is less invasive, generally painless, has no complications, and can effectively differentiate between structural causes (polyps, adenomyosis, leiomyoma, malignancy) and non-structural causes (ovulatory dysfunction, coagulopathy) of abnormal bleeding. 2

• The American College of Radiology designates TVUS as "usually appropriate" for initial imaging of abnormal uterine bleeding, with the highest appropriateness rating (7-9) among all imaging modalities. 1

Critical Pre-Contraception Assessment

• Before prescribing hormonal contraception, you must exclude structural pathology that could be masked by hormonal suppression of bleeding, particularly endometrial polyps, submucous fibroids, or premalignant lesions that require definitive diagnosis and treatment. 2, 4

• At age 41, this patient is perimenopausal with increasing risk of endometrial hyperplasia from anovulatory cycles and unopposed estrogen exposure, making structural assessment essential before initiating hormonal therapy. 2, 5

• Abnormal echogenicity and texture of the endometrium correlate with significant underlying uterine pathology even when thickness appears normal, information that guides whether endometrial sampling is needed. 6

Why Other Options Are Inappropriate

TSH (Option B) - Secondary Investigation

• TSH should be measured to assess endocrine contributors to ovulatory dysfunction, but this is a secondary laboratory test that does not exclude structural pathology requiring different management than contraception alone. 2

• Thyroid dysfunction causes ovulatory abnormal bleeding but does not preclude the need for imaging to rule out structural lesions that would contraindicate or complicate hormonal contraception. 5

FSH (Option A) - Not Indicated

• FSH measurement has no role in the initial evaluation of abnormal uterine bleeding in a 41-year-old woman, as it does not identify structural causes or guide contraceptive selection. 2

• Perimenopausal status is a clinical diagnosis based on menstrual pattern changes, not FSH levels, and FSH does not inform whether structural pathology is present. 4

Endometrial Biopsy (Option D) - Premature Without Imaging

• Endometrial biopsy is indicated when TVUS shows endometrial thickness ≥3-4mm in high-risk patients or when ultrasound findings suggest focal lesions, but performing biopsy before imaging is inefficient and may miss structural lesions requiring hysteroscopic evaluation. 2, 6

• Women ≥45 years with abnormal uterine bleeding should undergo endometrial sampling regardless of ultrasound findings, but at age 41 without additional risk factors (obesity, diabetes, Lynch syndrome, tamoxifen use), the decision for biopsy should be guided by ultrasound results. 2, 5

• Office endometrial biopsy has a 10% false-negative rate and may miss focal lesions such as polyps, making imaging essential to direct appropriate tissue sampling technique (blind biopsy vs. hysteroscopic directed biopsy). 2, 7

Algorithmic Approach

Step 1: Initial Imaging

• Perform transvaginal ultrasound combined with transabdominal approach to fully assess pelvic structures, evaluating endometrial thickness, texture, echogenicity, and presence of focal lesions (polyps, fibroids). 1, 2

Step 2: Interpretation and Next Steps

• If TVUS shows normal endometrium with no structural abnormalities: Proceed with contraceptive prescription and consider TSH/prolactin if anovulatory pattern suggests endocrine dysfunction. 2, 5

• If TVUS shows focal lesions or thickened/abnormal endometrium: Perform saline infusion sonohysterography (96-100% sensitivity for endometrial pathology) to better characterize findings. 2, 6

• If sonohysterography confirms polyps or submucous fibroids: Refer for hysteroscopic evaluation and directed biopsy before initiating hormonal therapy. 2, 6

• If TVUS cannot adequately visualize the endometrium due to body habitus, uterine position, or pathology (adenomyosis, large fibroids): Proceed directly to endometrial sampling. 1, 2

Step 3: Risk-Stratified Biopsy Decision

• Consider immediate endometrial biopsy if patient has risk factors for endometrial cancer: obesity (BMI >30), diabetes, hypertension, chronic anovulation, polycystic ovary syndrome, or family history of Lynch syndrome. 2, 5

Common Pitfalls to Avoid

• Never prescribe hormonal contraception without first excluding structural pathology, as bleeding suppression may delay diagnosis of polyps, fibroids, or premalignant lesions requiring surgical intervention. 2, 4

• Do not rely on endometrial thickness alone in premenopausal women, as normal thickness varies with menstrual cycle phase and pathology may be present even with thickness <5mm. 6

• Do not accept inadequate ultrasound visualization as reassuring—if the endometrium cannot be fully assessed, proceed to endometrial sampling or advanced imaging rather than empiric hormonal therapy. 1, 2

• Avoid performing endometrial biopsy before imaging in average-risk premenopausal women, as ultrasound findings direct the appropriate sampling technique and may identify lesions requiring hysteroscopic rather than blind biopsy. 2, 6, 7