Obstetric — 1st trimester — Reference values

Obstetric — 1st trimester — Reference values: Gestational sac visible (TV), Yolk sac visible, Embryo with heartbeat, Embryonic HR — poor prognosis.

Measurements and reference values

Measurement	Usual value	Note
Gestational sac visible (TV)	≈ 5,0 wk	2–3 mm sacSource: GLOWM / Ultrasoundpaedia
Yolk sac visible	MSD ≤ 10 mm	≈ 5.5–6 wkSource: GLOWM
Embryo with heartbeat	≈ 6 wk	usually by MSD 25 mmSource: Radiology Key
Embryonic HR — poor prognosis	< 90 bpm	in embryo < 8 wkSource: Medscape

Classifications and calculators

Calculator — nuchal translucency (11–13+6 wk)

NT	Reading
< 3.0 mm (CRL 45–84 mm)	Within expected; integrate into combined risk.
3,0–3,4 mm	Above the 95th percentile for most CRLs; weigh in risk.
≥ 3,5 mm	Increased risk (aneuploidy, cardiac, syndromes): counseling + diagnostic testing + fetal echo.

Only measure in the CRL 45–84 mm window, mid-sagittal plane, neutral fetus, adequate magnification. Secondary markers: absent nasal bone, tricuspid regurgitation, ductus venosus reversed a-wave.

Source: Fetal Medicine Foundation (FMF) / ISUOG guidelines

Criteria for NONVIABLE pregnancy (2012 consensus)

Finding	Conclusion
CRL ≥ 7 mm with NO heartbeat	Nonviable
MSD ≥ 25 mm with NO embryo	Nonviable
No embryo w/ HB ≥ 2 wk after sac without yolk sac	Nonviable
No embryo w/ HB ≥ 11 days after sac with yolk sac	Nonviable

Diagnostic (definitive) criteria from the 2012 SRU consensus. "Suspicious" findings warrant a follow-up scan.

Source: SRU Consensus 2012 (Doubilet et al.)

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