A 28-year-old woman comes to the office with her partner for evaluation of an inability to… — USMLE Step 2 CK

A 28-year-old woman comes to the office with her partner for evaluation of an inability to conceive for the past 14 months. She has a history of irregular menstrual cycles occurring every 35 to 90 days. Her last menstrual period was 10 weeks ago. Recently, she has felt unusually fatigued and has experienced mild nausea upon awakening. She takes a daily prenatal vitamin. Blood pressure is $112/70 \text{ mm Hg}$ , and pulse is $88/\text{min}$ . BMI is $27 \text{ kg/m}^2$ . Physical examination shows mild facial acne. Pelvic examination reveals a soft, slightly enlarged globular uterus and a bluish discoloration of the cervix. Laboratory studies obtained at a health fair last week show:

Thyroid-stimulating hormone (TSH): $0.1 \text{ mU/L}$ (N: $0.4-4.0 \text{ mU/L}$ )
Total thyroxine (T4): $13.5 \text{ \mu g/dL}$ (N: $5.0-12.0 \text{ \mu g/dL}$ )
Prolactin: $35 \text{ ng/mL}$ (N: $< 20 \text{ ng/mL}$ )

Which of the following is the most appropriate next step in management?

A
Initiation of letrozole therapy
B
Initiation of methimazole therapy
Urine human chorionic gonadotropin testingAnswer
D
Radioactive iodine uptake scan
E
Endometrial biopsy

Answer

Urine human chorionic gonadotropin testing

The correct next step is to perform a pregnancy test. Although this patient presents with a history of subfertility and irregular cycles suggestive of polycystic ovary syndrome (PCOS), her current symptoms (fatigue, morning nausea, 10 weeks of amenorrhea) and physical examination findings (Chadwick sign, Hegar sign) strongly point to an unconfirmed pregnancy. Furthermore, early pregnancy causes normal physiologic changes in thyroid and prolactin levels. The alpha subunit of hCG is structurally identical to TSH, leading to mild stimulation of the TSH receptor and a subsequent physiologic suppression of TSH. Estrogen increases thyroid-binding globulin (TBG) production, raising total T4 levels (while free T4 remains normal). Prolactin also rises physiologically to prepare for lactation. Recognizing these physiologic adaptations is critical to avoid unnecessary or harmful interventions, making a quantitative or qualitative human chorionic gonadotropin test the definitive next step.

Step-by-Step Solution

Analyze the patient's clinical presentation.

The patient has 10 weeks of amenorrhea, fatigue, morning nausea, a soft/enlarged uterus (Hegar sign), and a bluish cervix (Chadwick sign).

Identifying these classical signs and symptoms strongly suggests an early, unconfirmed pregnancy, despite her initial complaint of infertility.

Interpret the laboratory findings in the context of the clinical presentation.

Low TSH, high total T4, and mildly elevated prolactin are identified as normal physiologic adaptations to early pregnancy.

hCG shares an alpha subunit with TSH, stimulating the thyroid and suppressing endogenous TSH. Estrogen increases thyroid-binding globulin, elevating total (but not free) T4. Prolactin naturally rises during gestation.

Determine the most appropriate next step in management.

Select a simple pregnancy test (urine hCG).

Confirming the pregnancy is required before any further infertility workup or interventions, preventing contraindicated treatments like radioactive scans or ovulation induction.

Key Concept

Ruling out pregnancy is the mandatory first step in evaluating secondary amenorrhea and infertility, especially when accompanying physical and laboratory findings reflect normal physiologic changes of early gestation.

Estimated Time:1m 15s

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