Low-dose aspirin in pregnancy: indications, efficacy, safety, and remaining controversies

Aspirin is widely used in obstetric practice, but its effects in pregnancy depend strongly on indication, dose, and timing. Contemporary practice guidelines support low-dose aspirin for selected pregnant women at increased risk of preeclampsia, while historical reports of adverse outcomes often involve higher analgesic doses, prolonged exposure, or older non-selective NSAID-era data.

We conducted a narrative review of the literature on aspirin use in pregnancy and organized the evidence by study design and clinical theme, including mechanism of action, indications, efficacy, maternal safety, fetal safety, guideline recommendations, and ongoing research.

Evidence from randomized trials, meta-analyses, and guideline statements supports low-dose aspirin for prevention of preeclampsia in appropriately selected high-risk pregnancies. NICE recommends 75-150 mg daily from 12 weeks until birth in women at high risk or with more than one moderate risk factor, while US practice summaries of ACOG guidance describe 81 mg daily beginning after the first trimester for comparable risk groups. In the ASPRE trial, a 150 mg regimen begun between 11 and 14 weeks in screened high-risk women reduced preterm preeclampsia before 37 weeks by 62%. By contrast, several adverse outcomes cited in older literature involve high-dose aspirin or broader NSAID exposure and should not be extrapolated directly to current prophylactic low-dose use.

The evidence base supports low-dose aspirin for prevention of preeclampsia in appropriately selected pregnancies, with a generally favorable maternal and fetal safety profile when prescribed according to current guidance. Remaining questions concern optimal dose selection, adherence, aspirin resistance, and which subgroups derive most benefit from dose intensification or personalised prophylaxis.