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OB ultrasound

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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.

Labelled transvaginal ultrasound showing an inhomogeneous adnexal mass beside the ovary, with the uterus, an intrauterine device and coagulated blood markedTransvaginal · First trimester
source image carries labels

OB ultrasound · Ectopic pregnancy

Adnexal mass in a positive pregnancy test (labelled)

Diagnosis

Tubal ectopic pregnancy (blob sign) in a patient with an IUD

Normal against abnormal

The plane, and which way is up

Transvaginal, sweeping the uterus in sagittal and transverse, then each adnexa and the pouch of Douglas; transabdominal and the right upper quadrant when free fluid is suspected.

Look for, in order

  1. Empty uterus, or a thin decidua or a pseudosac (central, no double ring), in a woman with a positive test.
  2. An adnexal mass separate from the ovary: an inhomogeneous mass (the blob sign) or a ring with an echogenic rim (the bagel sign), with or without a yolk sac or embryo inside.
  3. Free fluid: a little in the pouch of Douglas is common; echogenic fluid, or fluid reaching Morison's pouch, means haemoperitoneum.
  4. The corpus luteum on the ovary is not the ectopic; it moves with the ovary when the probe presses.

What normal looks like

No intrauterine sac with an hCG above the discriminatory level, or an adnexal mass with a positive test, is ectopic until proven otherwise. A definite intrauterine pregnancy almost always excludes it, except after assisted reproduction.

Trap. A pseudosac in the cavity has fooled many: it is central, lacks the double decidual ring, and never contains a yolk sac.

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

  • An inhomogeneous mass adjacent to, and moving separately from, the ovary: the blob sign
  • An empty uterus with an intrauterine device in place
  • Echogenic fluid consistent with blood

What it means for the patient

The blob sign, an inhomogeneous adnexal mass separate from the ovary, is the most common appearance of a tubal ectopic; a bagel sign (a tubal ring) and a live ectopic with a heartbeat are the others. An IUD reduces the absolute risk of pregnancy, but a pregnancy that occurs with an IUD in place is more likely to be ectopic. Shown with the uploader's labels, for learning.

Framework: SOGC, Guideline: management of tubal ectopic pregnancy and pregnancy of unknown location (2024).

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