Question

The most important factor in hemostasis preventing PPH after placental separation is due to

• A. Uterine contraction and relaxation
• B. Retraction of the uterus
• C. Thrombosis of blood vessels in the myometrium
• D. Retroplacental clot

Hint:

Remember that retraction, unlike contraction, leaves the uterine muscle permanently short.

Answer 1

The Correct Option is B

This question checks whether we know the difference between a uterus that simply contracts and one that retracts, since only one of these truly stops bleeding after the placenta comes away.

1. Uterine contraction and relaxation: A contraction squeezes the vessels only while it lasts; once the muscle relaxes, the squeeze is gone. Bleeding could restart each time, so this cycle alone cannot explain lasting hemostasis.
2. Retraction of the uterus: Unlike a contraction, retraction leaves the muscle fibers permanently shorter after each wave. Since these fibers weave around the spiral arteries at the placental site, their lasting shortness clamps the vessels shut for good, acting like natural ligatures.
3. Thrombosis of blood vessels in the myometrium: Clot formation inside the compressed vessels does help seal them, but it can only happen once retraction has already narrowed the vessels; it is a helper step, not the main cause.
4. Retroplacental clot: This clot simply collects in the space left after separation. It is a sign that separation has happened, not the reason bleeding is controlled.

Retraction is what gives lasting compression of the vessels, so it is the key hemostatic factor.

Let's summarize:

• Contraction is temporary; retraction is a lasting shortening that keeps vessels pinched shut.
• Thrombosis and the retroplacental clot both depend on retraction happening first.

So the correct answer is retraction of the uterus.