Ultrasound — MCQs

Q: At how many days from the last menstrual period can fetal heart activity be detected earliest with transvaginal sonography?

46 days. **Explanation:** The detection of fetal heart activity is a critical milestone in early pregnancy ultrasound. In a normal pregnancy, the fetal heart begins to beat at approximately **5 to 6 weeks of gestation**. **1. Why 46 days is correct:** Using **Transvaginal Sonography (TVS)**, fetal cardiac activity can be detected when the embryo reaches a Crown-Rump Length (CRL) of 2–5 mm. Chronologically, this occurs at approximately **6 to 6.5 weeks** from the Last Menstrual Period (LMP). * 6 weeks = 42 days * 6.5 weeks = **45.5 days (rounded to 46 days)**. By 46 days, the heart tube has undergone folding and begins rhythmic contractions detectable by high-frequency TVS probes. **2. Analysis of Incorrect Options:** * **35 days (5 weeks):** At this stage, only the gestational sac is usually visible. The yolk sac appears around 5.5 weeks, but cardiac activity is generally not yet detectable. * **38 days (5.5 weeks):** This is the earliest the yolk sac is consistently seen. While the heart tube starts beating, it is often below the resolution threshold of most ultrasound machines. * **53 days (7.5 weeks):** By this time, cardiac activity is easily visible even on Transabdominal Sonography (TAS). This is too late to be considered the "earliest" detection point. **3. High-Yield Clinical Pearls for NEET-PG:** * **Order of appearance (TVS):** Gestational Sac (4.5–5 weeks) → Yolk Sac (5.5 weeks) → Embryo with Heartbeat (6–6.5 weeks). * **Discriminatory CRL:** If the CRL is **>7 mm** and no heartbeat is detected on TVS, it is diagnostic of pregnancy failure (per Society of Radiologists in Ultrasound criteria). * **TVS vs. TAS:** TVS can detect pregnancy milestones approximately **1 week earlier** than Transabdominal Sonography. * **Mean Sac Diameter (MSD):** A heartbeat should be visible when the MSD is >25 mm on TVS.

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Physics of Ultrasound

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Instrumentation and Techniques

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Abdominal Ultrasonography

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Pelvic Ultrasonography

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Obstetric Ultrasonography

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Small Parts Ultrasonography

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Musculoskeletal Ultrasonography

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Vascular Ultrasonography

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Pediatric Ultrasonography

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Contrast-Enhanced Ultrasound

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Ultrasound-Guided Interventions

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Doppler Ultrasound Principles and Applications

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Ultrasound — MCQs

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