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Difficulty: EasyMenstrual Cycle Abnormalities and Contraception

A 24-year-old woman comes to the clinic because she has not had a menstrual period for the past 3 months. Menarche occurred at age 12, and her menses had previously occurred at regular 28-day intervals. She has no other symptoms such as headaches, visual changes, or nipple discharge. She takes no daily medications and has no chronic medical conditions. She is sexually active with a male partner and relies on the withdrawal method for contraception. Vital signs include a temperature of 37.0°C (98.6°F), blood pressure of 118/76 mm Hg, pulse of 74/min, and BMI of 23 kg/m². Physical examination shows normal breast development, no hirsutism or acne, and a normal pelvic examination. Which of the following is the most appropriate initial step in evaluating this patient's condition?

  1. Measurement of serum human chorionic gonadotropinAnswer
  2. B
    Measurement of serum prolactin and thyroid-stimulating hormone levels
  3. C
    Pelvic ultrasonography
  4. D
    Endometrial biopsy
  5. E
    Administration of oral medroxyprogesterone acetate

Answer

Measurement of serum human chorionic gonadotropin
The patient meets the criteria for secondary amenorrhea, defined as the absence of menses for 3 or more months in a woman who previously had regular menstrual cycles. In any woman of reproductive age presenting with amenorrhea, the most common cause is pregnancy. Even with reported contraceptive use (especially unreliable methods like withdrawal), a pregnancy test (serum or urine beta-hCG) is the mandatory initial step. Only after pregnancy is ruled out should the physician proceed to evaluate other causes, such as thyroid dysfunction, hyperprolactinemia, or hypothalamic-pituitary-ovarian axis disorders.

Step-by-Step Solution

1
Identify the patient's primary presentation
The patient has secondary amenorrhea (absence of menses for ≥3 months in a woman with previously regular cycles).
Establishing the clinical definition guides the standardized diagnostic algorithm.
2
Determine the most common etiology
Pregnancy is the most common cause of secondary amenorrhea in women of reproductive age.
The withdrawal method of contraception has a high typical-use failure rate, increasing the probability of pregnancy in this sexually active patient.
3
Select the initial diagnostic test based on the etiology
A urine or serum beta-human chorionic gonadotropin (beta-hCG) test is required.
Pregnancy must be definitively ruled out before pursuing further endocrine, imaging, or pharmacological workup to avoid fetal harm and unnecessary testing.

Key Concept

The initial step in the evaluation of secondary amenorrhea in any woman of reproductive age is a pregnancy test (measurement of beta-hCG).
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Topics

Menstrual Cycle Abnormalities and Contraception

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