**Core Concept**
Mendelson's syndrome is a rare but life-threatening condition that occurs when sterile water aspirates into the lungs during pregnancy, leading to an acute chemical pneumonitis. This condition is often associated with women who have a preterm labor or an abortion, and it can cause severe respiratory distress and even death.

**Why the Correct Answer is Right**
Mendelson's syndrome occurs when the sterile water from the vagina and cervix enters the lungs, causing a chemical reaction that leads to inflammation and damage to the lung tissue. This condition is often seen in women who have had a preterm labor or an abortion, as the sudden rush of water from the vagina can cause the water to enter the lungs. The water contains enzymes and other substances that are not typically found in the lungs, and when these substances come into contact with the lung tissue, they can cause an immune response and inflammation.

**Why Each Wrong Option is Incorrect**
**Option A:** Hydrostatic pulmonary edema - This is a condition where fluid builds up in the lungs due to increased pressure, but it is not directly related to the aspiration of sterile water.

**Option B:** Pulmonary embolism - This is a condition where a blood clot forms in the lungs and blocks blood flow, but it is not related to the aspiration of sterile water.

**Option C:** Amniotic fluid embolism - This is a condition where amniotic fluid enters the bloodstream and causes an allergic reaction, but it is not directly related to the aspiration of sterile water.

**Clinical Pearl / High-Yield Fact**
It's essential to note that Mendelson's syndrome can occur in any woman who has had a preterm labor or an abortion, and it's crucial to be aware of this condition to provide prompt and appropriate treatment.

**Correct Answer: D. Aspiration of sterile water during pregnancy.**