Question

Which of these ectopic pregnancies is likely to progress for the maximum period?

• A. Isthmic
• B. Ampullary
• C. Interstitial
• D. Fimbrial

Hint:

Think about which part of the tube has the thickest, most stretchable wall around it.

Answer 1

The Correct Option is C

Step 1: Recall where ectopic pregnancies implant.
An ectopic pregnancy grows outside the uterine cavity, most often in the fallopian tube. The tube has different parts: the interstitial part running through the uterine wall, the isthmic part which is narrow, the ampullary part which is wider, and the fimbrial end near the ovary.

Step 2: Understand what decides how long a tubal pregnancy can grow.
How long an ectopic pregnancy survives before it ruptures depends mainly on how much the surrounding tissue can stretch and how thick and muscular that tissue is. A thicker, more distensible wall lets the pregnancy grow bigger and stay intact for longer before it tears through.

Step 3: Apply this to the interstitial site.
The interstitial part of the tube lies within the muscular wall of the uterus itself. Because this muscle tissue is thick and can stretch a lot, an interstitial ectopic pregnancy can keep growing for the longest time among the tubal sites, often reaching 3 to 4 months, before it finally ruptures.

Step 4: Rule out the isthmic site.
The isthmic part of the tube is narrow with a thin muscular wall, so an isthmic ectopic pregnancy ruptures earliest, usually around 6 to 8 weeks.

Step 5: Rule out the ampullary site.
The ampullary part is the widest part of the tube and is the most common site for ectopic pregnancy, but its wall is still much thinner than the uterine muscle, so it usually ruptures by about 8 to 12 weeks, earlier than an interstitial pregnancy.

Step 6: Rule out the fimbrial site.
The fimbrial end is the thin, finger like opening of the tube near the ovary. A pregnancy here has very little tissue to stretch into and is often expelled or aborts into the abdominal cavity early, well before an interstitial pregnancy would rupture.

Step 7: Final answer.
Because it sits inside the thick, distensible uterine muscle, the interstitial ectopic pregnancy can progress for the longest period.
\[ \boxed{\text{Interstitial}} \]