Question

Deep vein thrombosis is more common in the left leg because

• A. of dextrorotation of uterus
• B. the left common iliac vein is more tortuous
• C. inferior vena cava is on right side
• D. left ovarian artery is a branch of aorta

Hint:

Think about which direction the pregnant uterus usually rotates and which vein that puts pressure on.

Answer 1

The Correct Option is A

Deep vein thrombosis during pregnancy has a clear left-sided preference, and this comes down to how the pelvic blood vessels sit and how the uterus grows.

1. Dextrorotation of the uterus: As the uterus enlarges in pregnancy, it usually rotates toward the right. This extra rotation presses the uterus against the left common iliac vein, adding to the compression it already gets from the right common iliac artery crossing over it, which slows blood return from the left leg and favors clot formation there.
2. Left common iliac vein is more tortuous: There is no such inherent extra twisting of this vein compared to the right side, so this is not the real reason.
3. Inferior vena cava is on the right side: This is correct anatomy, but on its own it does not explain why the left leg specifically gets more clots.
4. Left ovarian artery is a branch of the aorta: This is also a true fact about pelvic anatomy, but it concerns arterial supply, not venous compression, so it does not explain the left leg pattern.

The compression from the crossing right common iliac artery, made worse by the uterus turning to the right in pregnancy, is what explains the higher rate of left leg DVT.

Let's summarize:

• The right common iliac artery normally crosses over the left common iliac vein.
• Dextrorotation of the pregnant uterus adds more pressure on this already crossed left vein.
• The other three options describe true facts that are not the direct cause of left-sided DVT.

So DVT is more common in the left leg because of dextrorotation of the uterus.