Low-Dose Aspirin Prophylaxis

Timing window and dose-response for aspirin prophylaxis against preeclampsia in high-risk pregnancy.

Current Stage

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Window timing

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TXA2 suppression

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Risk reduction est.

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Continuation

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Gestational week started12

Daily dose (mg)81

Thromboxane A2 (vasoconstriction)

Prostacyclin (vasodilation)

Aspirin / platelet COX-1

Spiral artery / placental bed

16-week critical window edge

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Identifying High-Risk Pregnancies for Aspirin Prophylaxis

High-risk criteria guide who should start prophylaxis early.

High risk: Prior preeclampsia (single major factor)
High risk: Chronic hypertension (single major factor)
≥2 needed: Moderate factors (combined threshold)
First visit: Screening timing (before 12–16 wks)

Major and moderate risk factors

Short placeholder: major factors alone qualify; moderate factors need combination.

The Critical Window — Starting Aspirin by 16 Weeks

Benefit depends heavily on starting before placentation completes.

12 wks: Ideal start (placeholder value)
16 wks: Latest effective (placeholder cutoff)
Low benefit: After 20 wks (placeholder estimate)
6–18 wks: Remodeling phase (placeholder range)

Why timing matters

Short placeholder: spiral artery remodeling finishes early, limiting later benefit.

Thromboxane A2 Suppression by Low-Dose Aspirin

Aspirin acetylates COX-1, blocking platelet thromboxane production.

COX-1: Target enzyme (platelet-specific)
81–150mg: Typical dose (placeholder range)
Platelet life: Effect duration (~7–10 days)
Relatively spared: Prostacyclin (endothelial COX-2)

Selective platelet inhibition

Short placeholder: low dose favors TXA2 suppression over prostacyclin loss.

Placental Vasodilation and Perfusion Improvement

Balance shift toward prostacyclin widens placental vessels.

Vasodilation: Vessel effect (placeholder summary)
Improved: Perfusion (placeholder summary)
↑: Placental blood flow (placeholder trend)
↓: Preeclampsia risk (placeholder trend)

From molecular shift to perfusion

Short placeholder: reduced vasoconstriction supports healthier placental blood flow.

Continuing Aspirin Through Delivery

Daily dosing typically continues into late pregnancy for sustained effect.

~36 wks: Stop point (placeholder guideline)
Daily: Adherence (placeholder requirement)
Low: Bleeding risk (placeholder note)
Unaffected: Delivery timing (placeholder note)

Sustained prophylaxis

Short placeholder: continuation maintains suppression until delivery.

Short placeholder: consistent daily dosing sustains protective effect.