A 32-year-old primigravida at 28 weeks of gestation presents with asymmetric intrauterine growth restriction (IUGR) confirmed on ultrasound. Doppler studies show abnormal umbilical artery waveforms with elevated pulsatility index. She is hemodynamically stable with normal blood pressure. Which drug is the first-line choice to improve fetal outcomes in this scenario?

Explanation

## First-Line Agent in IUGR with Abnormal Doppler **Key Point:** Low-dose aspirin (75–150 mg daily) is the first-line pharmacological agent for IUGR, particularly when abnormal umbilical artery Doppler waveforms are present. It improves placental perfusion and reduces the risk of adverse perinatal outcomes. ### Mechanism of Action in IUGR Aspirin works by: 1. Inhibiting thromboxane A₂ synthesis in platelets → reduced platelet aggregation 2. Promoting prostacyclin production in endothelium → vasodilation 3. Improving placental blood flow and reducing placental vascular resistance 4. Preventing placental infarction and thrombosis ### Evidence Base **High-Yield:** Multiple randomized trials (including CLASP and ASPRE trials) demonstrate that low-dose aspirin initiated in the second or early third trimester reduces the incidence of preeclampsia and IUGR by approximately 15–20% when abnormal Doppler findings are present. ### Timing and Dosing | Parameter | Details | |-----------|----------| | **Dose** | 75–150 mg daily | | **Timing** | Start as soon as IUGR + abnormal Doppler confirmed | | **Duration** | Continue until delivery | | **Safety** | Safe in pregnancy; no increased bleeding risk at low doses | **Clinical Pearl:** Aspirin is most effective when started early (before 16 weeks ideally, but still beneficial up to 28 weeks). In this patient at 28 weeks with confirmed abnormal Doppler, aspirin should be initiated immediately. ### Why Aspirin Over Other Antihypertensives - **Nifedipine, methyldopa, labetalol** are antihypertensive agents used when maternal hypertension is present, but this patient is normotensive - These agents do NOT directly improve placental perfusion in the absence of hypertension - Aspirin's mechanism is specifically directed at placental vascular pathology, not blood pressure control **Warning:** Do not confuse aspirin's role in IUGR prevention with its use in preeclampsia management. While both benefit from aspirin, the indication here is the abnormal Doppler waveform in a normotensive patient.