Transvaginal Ultrasound Before Prescribing Contraception
In a 41-year-old woman with six months of abnormal uterine bleeding requesting contraception, transvaginal ultrasound is the most appropriate initial investigation before prescribing hormonal contraception. 1
Rationale for Transvaginal Ultrasound as First-Line
The American College of Radiology designates transvaginal ultrasound (combined with transabdominal imaging) as the first-line diagnostic test for abnormal uterine bleeding in premenopausal women, assigning it the highest appropriateness rating (7–9) among all imaging modalities. 1
TVUS reliably distinguishes structural causes—including polyps, adenomyosis, leiomyomas, endometrial hyperplasia, and malignancy—from non-structural causes such as ovulatory dysfunction or coagulopathy. 1
At age 41 with six months of AUB, this patient requires structural evaluation before starting hormonal contraception, which could mask underlying pathology or delay diagnosis of premalignant/malignant conditions. 1, 2
Why Not Endometrial Biopsy First?
Endometrial biopsy is not the first investigation; it is indicated only after TVUS identifies concerning features (e.g., endometrial thickness ≥10 mm or focal lesions) or when the patient has high-risk factors for endometrial cancer. 1
The American College of Radiology recommends that the initial step remains TVUS to guide whether immediate endometrial biopsy is needed or whether hormonal management can proceed safely. 1
Women ≥45 years presenting with abnormal uterine bleeding should undergo endometrial sampling regardless of ultrasound findings, but at age 41, the decision is guided by TVUS findings and risk factors. 1
Practical Algorithm
Step 1: Order transvaginal ultrasound (combined with transabdominal imaging) to measure endometrial thickness and assess for structural lesions. 1
Step 2: Interpret TVUS findings:
- If endometrial thickness is <10 mm and no focal lesions are present, hormonal contraception may be prescribed without further imaging. 1, 3
- If endometrial thickness is ≥10 mm, focal lesions are identified, or the endometrium cannot be adequately visualized, proceed to endometrial sampling. 1, 3
Step 3: If TVUS suggests focal lesions (polyps, submucous fibroids), consider saline infusion sonohysterography, which demonstrates 96–100% sensitivity for detecting endometrial pathology. 1, 4
Step 4: If initial endometrial biopsy is non-diagnostic or symptoms persist despite normal TVUS, escalate to hysteroscopy with directed biopsy. 1
Why Not TSH or FSH?
TSH should be ordered to assess for thyroid dysfunction as a cause of ovulatory dysfunction, but it does not exclude structural pathology and should be performed concurrently with—not instead of—TVUS. 1, 4
FSH is not indicated in a 41-year-old woman with AUB requesting contraception; it does not guide the decision to prescribe contraception and does not exclude structural causes of bleeding. 5, 4
Critical Pitfalls to Avoid
Do not prescribe hormonal contraception without first excluding structural causes of AUB, as hormones may mask symptoms of endometrial hyperplasia or malignancy. 1, 2
Do not assume that age <45 years eliminates the need for structural evaluation—perimenopausal women with AUB have increasing rates of endometrial polyps, fibroids, and premalignant conditions. 2, 6
Do not accept inadequate TVUS visualization as reassuring; if the endometrium cannot be adequately assessed due to body habitus or uterine pathology, proceed directly to endometrial sampling. 1
In premenopausal women, normal endometrial thickness varies with menstrual cycle phase, and there is no validated absolute upper limit cutoff; abnormal echogenicity and texture correlate with significant pathology even when thickness appears normal. 7