A 28-year-old woman presents with amenorrhea of 6 weeks. Urine beta-hCG is positive. She has no risk factors for ectopic pregnancy. What is the investigation of choice to confirm intrauterine pregnancy and establish accurate dating?
A. Transvaginal ultrasound
B. Pelvic examination
C. Transabdominal ultrasound
D. Serum beta-hCG quantitation
Explanation
Investigation of Choice for Confirming Intrauterine Pregnancy and Dating
Key Point
Transvaginal ultrasound (TVS) is the gold standard for early pregnancy confirmation and accurate dating in the first trimester.
Why Transvaginal Ultrasound?
1.
Earliest detection: Gestational sac visible at hCG levels of 1,000–2,000 mIU/mL (around 4.5–5 weeks)
2.
Superior resolution: High-frequency probe (7–10 MHz) provides excellent visualization of early intrauterine pregnancy
3.
Accurate dating: Crown-rump length (CRL) measurement has ±3–5 days accuracy in first trimester
4.
Rules out ectopic pregnancy: Confirms intrauterine location, critical for safe management
5.
Non-invasive, safe: No radiation, no contrast agents
Comparison of Dating Methods
Table
Investigation
Timing
Accuracy
Purpose
Transvaginal ultrasound
4.5–14 weeks
±3–5 days
Gold standard for dating & location
Serum beta-hCG quantitation
Qualitative only
Cannot date
Confirms pregnancy, not dating
Transabdominal ultrasound
5–14 weeks
±1–2 weeks
Less sensitive in early pregnancy
Pelvic examination
Clinical
Unreliable
Confirms pregnancy clinically, not accurate dating
High-YieldNEET PG
In the first trimester (≤13 weeks + 6 days), TVS with CRL measurement is the most accurate method for pregnancy dating, with error margin of only ±3–5 days. This dating should NOT be changed by later scans.
Clinical Pearl
Even in low-risk patients, TVS is essential to exclude ectopic pregnancy, which can present with positive hCG and amenorrhea but no intrauterine gestational sac.
Williams Obstetrics 26e Ch 5
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