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OB ultrasound

33 studies11 challenges

Where is the pregnancy, how old is it, is it well: the questions each image answers, in the order the clinic asks them. Every image opens with how to read it; switch to Practice when you are ready to be tested.

Ultrasound of a fetal profile at eleven weeks with calipers across the fluid at the back of the neckMid-sagittal profile · 11+6 weeks

OB ultrasound · First-trimester screening

Screening scan at eleven weeks

Diagnosis

Increased nuchal translucency with absent nasal bone; chorionic villus sampling in this pregnancy showed trisomy 21

Normal against abnormal

The plane, and which way is up

Mid-sagittal of the fetus at 11 to 14 weeks (CRL 45 to 84 mm), the fetus filling most of the screen, in a neutral position with the nasal bone, the tip of the nose and the palate in view and the amnion separate from the skin of the neck.

Look for, in order

  1. The nuchal translucency: the black fluid space between the skin and the soft tissue over the cervical spine, measured at its widest with the callipers on the inner borders.
  2. The nasal bone: a bright line inside the skin line of the nose, brighter than the skin above it.
  3. Other early markers where trained: tricuspid flow, ductus venosus, the intracranial translucency.

What normal looks like

A nuchal translucency below the 95th centile for the CRL (roughly under 3 mm at 12 weeks) and a nasal bone present. The measurement is combined with maternal age and serum markers; it is a risk, not a diagnosis.

Trap. Measuring the amnion instead of the skin, a flexed neck, or a poorly magnified image all change the reading by the fractions of a millimetre that matter.

Describe it in this order

  1. The plane and the approach (transabdominal or transvaginal)
  2. Location of the pregnancy: in the uterus or not
  3. Number: singleton or multiple, and chorionicity
  4. Viability: cardiac activity
  5. Dating or growth: the measurement that fits the stage
  6. Fetal anatomy, placenta, cord, fluid, cervix, as the stage allows
  7. Adnexa and free fluid
  8. Then, and only then, the impression

Findings

  • Nuchal translucency increased for gestational age
  • Nasal bone not visualised

What it means for the patient

An increased nuchal translucency is a screening finding, not a diagnosis. It raises the risk of trisomies 21, 18 and 13, of structural heart defects and of some genetic syndromes, and the next step is a conversation: diagnostic testing (CVS or amniocentesis) or cell-free DNA, plus a detailed anatomy scan and fetal echocardiography whatever the karyotype.

Framework: ISUOG, Practice guidelines: first-trimester and mid-trimester fetal ultrasound (2022).

OBGynSpace Tutor

It coaches the description; it does not read the image for you and will not name the diagnosis before you commit.