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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 showing a fetal head surrounded by a large volume of dark amniotic fluid within the uterusTransabdominal · Third trimester

OB ultrasound · Amniotic fluid

Fetal head surrounded by fluid

Diagnosis

Polyhydramnios

Normal against abnormal

The plane, and which way is up

Transabdominal, probe perpendicular to the floor, the uterus divided into four quadrants around the umbilicus, measuring the deepest vertical pocket of fluid free of cord and limbs in each.

Look for, in order

  1. The single deepest pocket (2 to 8 cm is normal), or the four-quadrant index (5 to 25 cm).
  2. Cord and limbs in the pocket do not count; use colour Doppler to be sure.
  3. With too much fluid: look for a reason (diabetes, a fetal anomaly of swallowing or the gut, twins, infection); with too little: rupture of membranes, growth restriction, the renal tract, the placenta.

What normal looks like

A deepest pocket of 2 to 8 cm. Oligohydramnios is under 2 cm; polyhydramnios is over 8 cm (or an index over 25).

Trap. Pressing the probe compresses the pocket; angling it exaggerates it. The deepest pocket is measured vertically.

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

  • Abundant anechoic fluid around the fetus
  • The fetus does not fill the anteroposterior diameter of the cavity

What it means for the patient

A second view: the fetus floats in an excess of fluid. Estimate the deepest vertical pocket at right angles to the floor, without cord or limbs in the pocket.

Framework: Cunningham et al., Williams Obstetrics, 26th edition (maternal physiology, labour mechanics, placental anatomy) (2022).

OBGynSpace Tutor

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