Measure crown–rump length to date, nuchal translucency to FMF standards for screening, and survey the early anatomy — skull, brain, heart, abdominal wall, limbs — where many major anomalies are already visible.
Orient first
- CRL 45–84 mm defines the window for NT measurement (verify local protocol).
- NT is measured in a mid-sagittal plane, fetus neutral, magnified so the head and upper thorax fill the image, callipers on-to-on.
- Acrania, holoprosencephaly, omphalocele, gastroschisis, megacystis and body-stalk anomaly can be diagnosed now.
Acquire the study
- Transabdominal ultrasound (transvaginal if needed); FMF-certified NT technique; mid-sagittal, axial and coronal views of the fetus.
The manoeuvre
- CRL in mm in a mid-sagittal plane with the fetus in a neutral position; derive gestational age.
- NT: maximum thickness in mm with callipers on the inner borders, amnion separate from skin.
- Head in axial plane: ossified skull, midline falx, butterfly choroid plexuses; intracranial translucency.
- Abdominal wall and cord insertion in the axial plane; stomach on the left; bladder (< 7 mm longitudinal — verify).
- Four limbs with three segments each; heart axis and four-chamber view where possible.
- Chorionicity in twins (lambda vs T sign).
What confirms it
- A dated pregnancy with NT measured to standard and an early anatomy survey documented.
What licenses you to exclude it
- A normal early survey does not exclude anomalies seen only later — the mid-trimester scan remains necessary.
The classic misread
- Measuring NT with the fetus hyperextended or confusing amnion with skin.