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These 10 free OB-1T questions are organized by exam domain, so you can see how each part of the POCUS - Obstetrics - First Trimester (OB-1T) blueprint is tested. Reveal the answer and explanation under each question.
An apparent gestational sac is visible beside the endometrial stripe in a single longitudinal transabdominal image. The patient is stable, and the probe marker points toward her head. To assess the collection's relationship to the endometrium, what should the operator acquire next?
Correct answer: B - An orthogonal transverse sweep through the collection and the uterine cavity.
During a first-trimester transvaginal examination, a thick-walled cystic lesion is found in the right adnexa. No yolk sac or embryo is visible within it. The operator is distinguishing a corpus luteum from a tubal gestational sac. Which finding provides the strongest anatomical evidence of ovarian origin?
Correct answer: C - Ovarian tissue partially surrounds and is continuous with the lesion.
A 12-week twin examination shows two fetuses with cardiac activity and what appears to be one placental mass. At the intertwin membrane's placental insertion, a triangular wedge of chorionic tissue extends between the amniotic layers. The membrane is clearly visualized throughout its course. How should chorionicity and amnionicity be recorded?
Correct answer: C - Dichorionic diamniotic.
On a magnified transvaginal view of a 7-week pregnancy, a thin membrane encloses the embryo. A separate 3-mm round structure has an echogenic rim and an anechoic center; it lies outside that membrane but inside the gestational sac. Which label belongs on the small round structure?
Correct answer: A - Yolk sac.
At an initial diagnostic transvaginal examination, a normally positioned intrauterine gestational sac contains no embryo. Its three orthogonal inner diameters are 18, 22, and 26 mm. Measurements including the echogenic rim are 24, 28, and 32 mm. No earlier ultrasound is available. Select the correctly calculated mean sac diameter and its interpretation under SRU criteria.
Correct answer: A - 22 mm; the findings are concerning for, but not diagnostic of, early pregnancy loss.
While examining a rounded ovarian cyst, the operator sees narrow dark bands extending behind its lateral margins. Tissue directly behind the cyst's center is brighter than adjacent tissue, and no calcification is visible in the wall. The dark bands shift when the insonation angle changes. What causes the lateral bands?
Correct answer: B - Refraction of the ultrasound beam at the curved cyst margins.
A patient's first dating scan is performed at 10 weeks 4 days by a certain last menstrual period, with regular 28-day cycles and no assisted reproduction. Properly obtained crown-rump length measurements correspond to 9 weeks 5 days; cardiac activity is present. Applying ACOG's first-trimester redating recommendations, how should the estimated due date be assigned?
Correct answer: D - Retain the menstrual estimate because the discrepancy does not exceed the applicable threshold.
A patient with mild spotting remains hemodynamically stable during follow-up. Serum hCG rises from 2,400 to 3,600 mIU/mL over 48 hours. Diagnostic transvaginal examinations at both visits show neither an intrauterine sac nor a suspicious adnexal lesion; no free fluid is present. Which conclusion best integrates the laboratory trend with the imaging?
Correct answer: B - An ongoing intrauterine pregnancy remains possible, but its location is still unknown.
After embryo transfer, a patient at 7 weeks develops focal left pelvic pain. Transvaginal ultrasound demonstrates an embryo with cardiac activity in a normally implanted intrauterine sac. A separate left adnexal sac contains a yolk sac, and the left ovary is clearly seen apart from that sac. What diagnosis accounts for both implantation sites?
Correct answer: D - Heterotopic pregnancy.
One week ago, ultrasound documented a normally implanted intrauterine gestational sac containing a yolk sac. After several hours of cramping and bleeding, the patient passed tissue; the pain has resolved and bleeding is now scant. A diagnostic transvaginal examination shows no gestational sac or residual intracavitary tissue, and the adnexa are unremarkable. Which diagnosis is supported by this sequence?
Correct answer: A - Completed early pregnancy loss.
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