**Core Concept**
Pre-eclampsia or pregnancy-induced hypertension (PIH) is a pregnancy complication characterized by high blood pressure and often accompanied by significant amounts of protein in the urine. The exact cause of PIH remains unknown, but it is believed to be associated with abnormal placentation, leading to endothelial dysfunction and a cascade of pro-inflammatory and pro-thrombotic responses.

**Why the Correct Answer is Right**
Low-dose aspirin has been shown to reduce the risk of developing PIH in high-risk pregnancies. This effect is thought to be due to its antiplatelet and anti-inflammatory properties, which help to prevent the formation of thrombi in the placental vasculature and reduce the release of pro-inflammatory cytokines. By modulating these pathways, aspirin helps to maintain endothelial function and reduce the risk of PIH.

**Why Each Wrong Option is Incorrect**
**Option A:** Calcium supplements have been studied as a potential preventive measure for PIH, but the evidence is limited and inconclusive. While calcium may have some benefits for maternal and fetal health, it is not a proven preventive measure for PIH.
**Option B:** High-dose vitamin C has been suggested as a potential preventive measure for PIH, but there is no strong evidence to support its use. Vitamin C may have some antioxidant effects, but it is not a proven preventive measure for PIH.
**Option C:** Bed rest has been recommended for women at risk of PIH, but there is no evidence that it is effective in preventing the condition. In fact, bed rest may even be counterproductive, as it can lead to muscle atrophy and decreased mobility.

**Clinical Pearl / High-Yield Fact**
Low-dose aspirin should be considered for high-risk pregnancies, particularly those with a history of PIH or other complications. A loading dose of 150mg followed by 75mg daily is a common regimen.

**Correct Answer:** D. Low-dose aspirin.