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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 the placenta with colour Doppler showing the umbilical cord vessels entering the middle of the placental surfaceTransabdominal with colour Doppler · 20+4 weeks

OB ultrasound · Placenta

Placenta with colour Doppler at twenty weeks

Diagnosis

Normal central placental cord insertion, three-vessel cord

Normal against abnormal

The plane, and which way is up

Transabdominal, then transvaginal for the lower edge: the placenta as a homogeneous grey plate with a bright chorionic plate on the fetal side and the retroplacental space on the uterine side.

Look for, in order

  1. Where is it? Anterior, posterior, fundal, and its relation to the internal os: covering, reaching, or clear by more than 20 mm.
  2. The cord insertion: central, marginal or velamentous, best shown with colour Doppler.
  3. Its texture and thickness: lakes and calcification are common late; a thick heterogeneous placenta with a haematoma behind it is the picture of abruption, though abruption is a clinical diagnosis.
  4. In a previous caesarean with an anterior low placenta: loss of the clear zone, lacunae and bladder wall interruption suggest accreta.

What normal looks like

A placenta clear of the os, with a central cord insertion, of thickness roughly the weeks in millimetres; a low placenta at 20 weeks usually migrates and is re-checked at 32 weeks.

Trap. A full bladder or a contraction can create a false low-lying placenta; empty the bladder and look again.

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

  • Central cord insertion into the placenta
  • Three vessels in the cord (two arteries, one vein) on colour flow

What it means for the patient

The cord insertion is documented at the anatomy scan. A velamentous insertion (into the membranes) or a marginal one matters for growth and, near the cervix, for vasa praevia. The three-vessel count is confirmed in the same view or on an axial section of the cord.

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

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