## Timing of Fetal Cardiac Activity on Transvaginal USG **Key Point:** Fetal cardiac activity is first detectable on transvaginal ultrasound at **6–7 weeks of gestation** (measured from the last menstrual period). ### Landmarks by Gestational Age | Gestational Age | Transvaginal USG Finding | | --- | --- | | 4–5 weeks | Gestational sac only; yolk sac may appear | | 6–7 weeks | **Fetal pole with cardiac activity** | | 8–9 weeks | Clear fetal anatomy; heart rate 150–180 bpm | | 10–11 weeks | Nuchal translucency measurable; crown-rump length | ### Clinical Significance **High-Yield:** The presence of cardiac activity at 6–7 weeks is a reassuring sign of a viable intrauterine pregnancy and helps exclude: - Ectopic pregnancy - Blighted ovum (anembryonic gestation) - Miscarriage **Clinical Pearl:** Absence of cardiac activity in a fetal pole >6 mm on transvaginal scan suggests fetal demise or incorrect dating; repeat scan in 1–2 weeks is recommended before counselling pregnancy loss. **Tip:** Remember the rule: **Fetal pole at 5–6 weeks, cardiac activity at 6–7 weeks.** This is a high-yield dating landmark for NEET PG. [cite:Callen's Ultrasound in Obstetrics and Gynecology 6e Ch 3] 
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