4. 1st Trimester Obstetric/OB Ultrasound Protocol

Ectopic Pregnancies

An ectopic pregnancy refers to any pregnancy occurring outside of the uterus. They pose a substantial risk to the mother and thus must be diagnosed accurately. Ectopic pregnancies cannot be missed.

  • These patients commonly present with abdominal painpelvic pain, or vaginal bleeding.
  • Presentations that increase concern:
    • Peritoneal irritation
    • Cervical motion tenderness
    • Lack of fetal heart tones
  • Risk factors:
    • Previous tubal surgery
    • Prior ectopic pregnancy

The vast majority of ectopic pregnancies are found in the fallopian tubes, particularly in the ampullary region of the tube. They can be seen in many different locations, however. Because there are many places in which an ectopic pregnancy can be, the primary goal of ultrasound should be not to definitively rule in an ectopic pregnancy, but rather to rule in an intrauterine pregnancy; therefore making an ectopic pregnancy highly unlikely.

Ectopic Pregnancy Locations

Follow these steps to look for an ectopic pregnancy:

Step 1  Scan the uterus for a gestational sac with a yolk sac, fetal pole, or cardiac activity within the uterus. If detected then the patient has IUP and unlikely a concurrent ectopic (unless IVF therapy)

  • Step 2 – if no IUP detected then scan adnexa for direct signs of ectopic pregnancy.
    • The tubal ring sign  is a common ultrasound finding with an ectopic pregnancyThis is a thick hyperechoic ring around a tubal mass.
    • The ring of fire sign can be seen in ectopic pregnancy but can also be seen in corpus luteum cysts. The ring of fire sign describes the high-velocity flow seen on color Doppler imaging due to the high vascularization of the area surrounding the ectopic pregnancy.
    • Finding a gestational sac and fetal pole with cardiac activity outside of the uterus is diagnostic of an ectopic pregnancy.
Tubal Ring Sign Ectopic Pregnancy OB Obstetric Obstetrical Ultrasound
Thick echogenic ring around a tubal mass (left side). It is more echogenic than the corpus luteum (right side).
Ring of Fire Sign Ectopic Pregnancy OB Obstetric Obstetrical Ultrasound
Ring of fire sign in an ectopic pregnancy.

Step 3  Assess the Pouch of Douglas for free fluid.

Step 4 – Integrate ultrasound findings with B-hCG levels

  • Normal IUP
    • Fetus visible in the uterus
    • B-hCG level of 1000-2000 mIU/mL
  • Suspicious for Ectopic
    • Ectopic mass
    • Fluid in the cul de sac
    • Absent IUP
    • Abnormal serum B-hCG pattern*

*Normally, B-hCG levels rise at least 50% in a 48 hour period. In ectopic pregnancies, B-hCG levels commonly rise 50% or less in the same timeframe. Additionally, B-hCG levels plateau sooner than IUPs (IUPs usually plateau at around 10-12 weeks).

Ectopic Pregnancy Algorithm OB Obstetric Obstetrical Ultrasound

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