Interpreting the early pregnancy scan and the hCG pair — structured oral station (12 minutes)

Opening prompt — "Interpret this scan for me."

Model response — classify first, then say what is missing from the report. [1][2]

• "There is an intrauterine gestational sac, so this is an intrauterine pregnancy of uncertain viability, not a pregnancy of unknown location. At a mean sac diameter of 12 mm with no yolk sac, it is well below the 25.0 mm threshold, so I cannot diagnose a failed pregnancy today."[1]
• "My management is a repeat transvaginal scan a minimum of 7 days after the first, and I would tell her that further scans may still be needed."[1]
• "But the report is incomplete in a way that matters. It describes the right ovary and does not describe the left adnexum at all, and this is a frozen embryo transfer pregnancy. I want that adnexum imaged before anybody reassures her."[2]

Examiner is listening for: the correct category, the exact millimetre threshold, the 7-day minimum, and — the discriminator of a strong candidate — noticing the unexamined adnexum after assisted reproduction. [1][2]

Probe 1 — "Why does the assisted reproduction matter?"

• "Because an intrauterine pregnancy does not exclude an ectopic one. Heterotopic pregnancy is uncommon spontaneously but is considerably more likely after assisted reproduction, and the guidance is explicit that you scan the uterus and the adnexae to look for it."[2]
• "She also has free fluid in the Pouch of Douglas and pelvic discomfort. A small amount of anechoic fluid is often physiological, but combined with an unexamined adnexum and a transfer pregnancy, I am not willing to attribute it without looking."[2][3]

Probe 2 — "Her hCG is 4100 and there is no yolk sac. Does that not tell you the pregnancy has failed?"

The second trap. Decline it and give the numbers. [1][4]

• "No. hCG is not a viability criterion, and it is not a location criterion either. The diagnosis of failure is made on the ultrasound measurements — mean sac diameter of 25.0 mm or more with no embryo, or crown–rump length of 7.0 mm or more with no heartbeat."[1]
• "And the level itself is a poor discriminator. In a prospective multicentre cohort, 11% of women with an hCG above 3000 IU/L still had a viable intrauterine pregnancy."[4]
• "Her conception date is known precisely because it was an embryo transfer, so I would rather calculate the true gestation from the transfer date than argue from the hormone at all."[6]

Probe 3 — "The sonographer measured 12 mm. Your colleague measures 15 mm. Does that change anything?"

• "Not the management, and that is the point. Both are far below 25 mm, so the plan is unchanged."[5]
• "It does illustrate why the thresholds carry headroom. Intra- and interobserver reproducibility of transvaginal sac measurement spans several millimetres, which is exactly why we do not act on a single borderline number — we take a second opinion or a second scan."[5]

Probe 4 — "Suppose the repeat scan in a week shows a crown–rump length of 6 mm with no heartbeat. What then?"

• "Six millimetres is below the 7.0 mm threshold, so I still cannot diagnose a failed pregnancy. I would rescan a minimum of 7 days later again, or seek a second opinion."[1]
• "If instead the crown–rump length were 7.0 mm or more with no heartbeat, I would either get a second opinion on viability or repeat the scan a minimum of 7 days after the first before making the diagnosis. I would not diagnose it on that single image alone."[1]
• "And I would not use her dates to override the measurements. Gestational age from the last menstrual period must not be used to decide whether a heartbeat should be visible."[1]

Probe 5 — "Tell me what a pseudosac is and why you care."

• "It is a collection of fluid in the uterine cavity that can be mistaken for an early gestational sac. It sits centrally in the midline cavity with a single thin outline, often teardrop-shaped, and it never develops a yolk sac."[2]
• "A true sac sits eccentrically within the endometrium and shows the double decidual sign — a hypoechoic structure surrounded by two concentric echogenic rings."[2][3]
• "I care because reporting a pseudosac as an intrauterine pregnancy sends a woman home with an untreated tubal ectopic and a false sense of safety."[2]

Probe 6 — "She asks whether waiting a week could harm the pregnancy. What do you say?"

Communication is scored. Use her words, not ours. [1]

• "Waiting does not harm the pregnancy. If it is going to grow, it grows whether we scan you or not; if it is not, the week does not change that either."
• "What the week does is stop us being wrong. The measurements we use were deliberately set so that we almost never tell someone they have miscarried when they have not."[1]
• "Meanwhile, here is what to watch for and the number to call at any hour." Then give the return criteria explicitly.[2]

Probe 7 — "Her repeat hCG at 48 hours is 4900. Comment."

• "That is a rise of about 19.5%, which is well below the 63% threshold and below even the slowest rise compatible with a viable intrauterine pregnancy, which is roughly 53% over two days."[7]
• "In a woman with an intrauterine sac that is a poor prognostic sign, but it is not by itself a diagnosis. My action is clinical review and a scan that examines both adnexae, because the failing sac and a coexisting ectopic pregnancy are not mutually exclusive here."[7][2]