Interstitial ectopic pregnancy differs from ampullary ectopic pregnancy in which clinically important way?

• A Presents earlier at 4–5 weeks due to poor vascular supply
• B Does not respond to methotrexate and always requires laparotomy
• C Is always associated with a normal intrauterine echogenic ring on ultrasound
• D Ruptures later (8–16 weeks) with massive hemorrhage due to rich myometrial blood supply ✓

Explanation

Interstitial (cornual) ectopic pregnancy implants within the intramural portion of the fallopian tube in the uterine wall, which has an abundant blood supply from both uterine and ovarian arteries. As a result, it grows undetected for longer than ampullary ectopics and when it ruptures — typically at 8–16 weeks — the hemorrhage is catastrophic and potentially fatal. Methotrexate can be used for unruptured interstitial ectopics with favorable criteria. On ultrasound, there is no intrauterine gestational sac; the chorionic villi are eccentrically placed in the cornual region.

Reference: Williams Obstetrics, 26th ed.

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Written and medically reviewed by the StethoPrep medical team.