This week, we are sharing another USMLE® Step 1-style practice question to test your knowledge of medical topics. Today’s case focuses on a 73-year-old woman with shortness of breath. Past medical history is notable for hypertension, chronic obstructive pulmonary disease, and type II diabetes mellitus. Can you figure it out?
A 32-year-old woman comes to the obstetrician with her partner for evaluation of infertility. The patient has had three prior pregnancies, all of which ended in miscarriages during the first trimester. She currently has monthly menstrual periods. Past medical history is unremarkable. The patient is an avid runner and takes part in several marathons each year. Temperature is 37.2°C (99.0°F), blood pressure is 115/78 mmHg, pulse is 72/min, and body mass index is 21 kg/m2. Speculum examination reveals a normal-appearing cervix. The abdomen is soft and non-distended, and there are no palpable masses. The remainder of the physical examination is unremarkable. Laboratory testing reveals a prothrombin time of 12 seconds and a partial thromboplastin time of 37 seconds. A hysterosalpingogram is performed and shown below. Which of the following best describes the pathophysiology of this patient’s condition?
A. Complete failure of Müllerian duct fusion
B. Proliferation of benign uterine smooth muscle tumors
C. Formation of anti-β2 glycoprotein autoantibodies
D. Incomplete fusion of the Müllerian ducts
E. Reduced hypothalamic hormone release
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The correct answer to today’s USMLE® Step 1 Question is…
D. Incomplete fusion of the Müllerian ducts
Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
The incorrect answers to today’s USMLE® Step 1 Question are…
A. Complete failure of Müllerian duct fusion
Incorrect: Uterus didelphys occurs when there’s complete failure in fusion of the Müllerian ducts. As a result, individuals will have two uteruses, two cervixes, and two vaginas. In contrast, this patient’s imaging demonstrates a single vagina and cervix but two uteruses, which is more suggestive of a bicornuate uterus.
B. Proliferation of benign uterine smooth muscle tumors
Incorrect: Uterine fibroids are caused by benign proliferation of smooth muscle. The condition can lead to recurrent miscarriages. However, fibroids are neither present on physical examination nor imaging, and the patient lacks additional symptoms suggestive of fibroids (e.g., menorrhagia, back pain).
C. Formation of anti-β2 glycoprotein autoantibodies
Incorrect: Individuals with antiphospholipid syndrome can form anti-β2 glycoprotein autoantibodies and are at risk for recurrent miscarriages. The condition will lead to an elevated partial thromboplastin time (PTT). In contrast, this patient’s PTT is within normal limits, making antiphospholipid syndrome unlikely.
E. Reduced hypothalamic hormone release
Incorrect: Excessive exercise can lead to reduced hypothalamic secretion of GnRH, which subsequently impairs pituitary release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The condition can manifest with amenorrhea and infertility. While this patient has a history of training for marathons, her BMI is within normal limits, and she has been having monthly menstrual periods. Furthermore, imaging findings are more suggestive of a uterine abnormality as the underlying cause of her prior miscarriages.
Main Explanation
This patient has a history of recurrent miscarriages. Laboratory testing is unremarkable, and imagining reveals a bicornuate uterus. This condition arises due to incomplete fusion of the Müllerian ducts.
Uterine anomalies describe anatomical malformations of the uterus that are present at birth.
A septate uterus occurs when the Müllerian ducts fuse, but the septum between the ducts persists. The condition can lead to decreased fertility and an increased risk of early miscarriage or pregnancy loss. Diagnosis can be made with imaging techniques (e.g., ultrasound, hysterosalpingogram, MRI) revealing the presence of a midline septum.
A bicornuate uterus occurs due to incomplete fusion of the Müllerian ducts. As a result, the uterus develops two upper horns above the uterine body, giving it a heart shape. The finding can be observed on imaging. The condition can lead to an increased risk of complicated pregnancy, fetal malpresentation, early miscarriage, and preterm birth. Finally, uterus didelphys occurs due to complete failure of Müllerian duct fusion. As a result, patients will have a double uterus, double cervix, and double vagina. While pregnancy remains possible, patients are at increased risk of early miscarriage and preterm birth. Imaging will reveal two uncommunicated uteruses, each one with its own fallopian tube.
Major Takeaway
Uterine anomalies include septate uterus, bicornuate uterus, and uterus didelphys. These conditions can be diagnosed via imaging (e.g., ultrasound, hysterosalpingogram, MRI). Affected patients are at an increased risk of miscarriage and preterm birth.
References
Hassan, M.M., Lavery, S.A., Trew, G.H. (2010) Congenital uterine anomalies and their impact on fertility. Women’s Health. 6(3), 443-461. Doi: 10.2217/whe.10.19.
Kaur, P., Panneerselvam, D. (2021) “Bicornuate uterus”. Stat Pearls [Internet]. Web Address: https://www.ncbi.nlm.nih.gov/books/NBK560859/. _________________________
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The United States Medical Licensing Examination (USMLE®) is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). Osmosis is not affiliated with NBME nor FSMB.
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