What is the most important test to do before starting oral contraceptive pills (OCP) in a patient with abnormal uterine bleeding (AUB)?

Most Important Test Before Starting OCP for AUB

The most important test before starting oral contraceptive pills in a patient with 6 months of abnormal uterine bleeding is pelvic ultrasound (transvaginal with transabdominal approach), not endometrial biopsy, FSH, or LH.

Rationale for Pelvic Ultrasound as First-Line

Transvaginal ultrasound with Doppler is the first-line imaging study for all patients with abnormal uterine bleeding before initiating oral contraceptives 1. This approach is critical because:

• Starting OCPs without imaging risks missing serious pathology that would be temporarily suppressed by hormonal contraception, delaying diagnosis of conditions like endometrial cancer or significant structural lesions 1
• Combined transabdominal and transvaginal ultrasound provides comprehensive evaluation of the uterus and adnexa, identifying structural causes including polyps, adenomyosis, leiomyomas, and endometrial hyperplasia/malignancy 2, 1
• The ultrasound findings will guide whether endometrial biopsy is subsequently needed 1

Why Not the Other Options?

FSH and LH (Options A & B)

• Hormonal testing such as FSH and LH does not contribute substantially to safe oral contraceptive initiation according to CDC contraceptive guidelines 1
• These tests are classified as "Class C" (not contributing substantially to safe contraceptive use) in the U.S. Selected Practice Recommendations 1
• Among healthy women, no examinations or tests are needed before OCP initiation, though women with known medical problems may need additional evaluation 1

Endometrial Biopsy (Option D)

• Endometrial biopsy is not the first test—it is indicated based on age and ultrasound findings 1
• Biopsy is required for women ≥35 years or younger women with risk factors for endometrial cancer, and its need is guided by ultrasound findings 1
• In perimenopausal women with AUB, endometrial biopsy is required, but the question doesn't specify age 2

Clinical Algorithm

1. Obtain pelvic ultrasound first (transvaginal and transabdominal with Doppler) to assess endometrial thickness and architecture, identify structural lesions, and evaluate for masses 1

2. Perform pregnancy test (β-hCG) as part of pre-treatment workup 3

3. Consider endometrial biopsy if:

   • Patient is ≥35 years old 1, 4
   • Patient has risk factors for endometrial cancer (obesity, diabetes, hypertension, unopposed estrogen exposure) 2
   • Ultrasound shows focal endometrial abnormality or thickened endometrium 2

4. Additional testing as indicated: TSH, prolactin based on clinical presentation 1

Important Caveat

A speculum or bimanual examination is considered unnecessary before prescribing oral contraceptive pills 5. The package insert for OCPs specifically states that a gynecologic examination is not necessary, as there is nothing found on pelvic examination that would be a contraindication to prescribing OCPs 5. However, this refers to the physical examination, not imaging studies—ultrasound remains essential to exclude structural pathology before masking symptoms with hormonal therapy 1.

Answer: C. Pelvic US