ASA Use in Pregnancy
Low-dose aspirin (81-100 mg daily) should be initiated between 12-16 weeks of gestation and continued until delivery in pregnant women with high-risk factors for preeclampsia, including history of preeclampsia, antiphospholipid syndrome, autoimmune disease, chronic hypertension, renal disease, type 1 or 2 diabetes, or multifetal gestation. 1, 2
Indications for Low-Dose Aspirin
High-Risk Conditions (Strong Recommendation)
For women with antiphospholipid syndrome (APS), aspirin must be combined with prophylactic-dose heparin (usually LMWH) throughout pregnancy and 6-12 weeks postpartum. 3 This combination therapy is strongly recommended for obstetric APS based on moderate-strength evidence showing improved live birth rates, though pregnancy loss still occurs in 25% despite treatment. 3
For pregnant women with systemic lupus erythematosus (SLE), low-dose aspirin (81-100 mg daily) should be started in the first trimester as these patients have significantly elevated preeclampsia risk. 3 The American College of Rheumatology conditionally recommends this approach, noting that doses up to 150 mg have been studied but lack comparative data showing superiority over 81-100 mg doses. 3
Women with history of early-onset preeclampsia requiring delivery before 34 weeks, or more than one prior pregnancy complicated by preeclampsia, should receive daily low-dose aspirin starting between 12-28 weeks (optimally before 16 weeks) and continuing until delivery. 1, 2
Moderate-Risk Conditions (Conditional Recommendation)
Low-dose aspirin prophylaxis should be considered when two or more moderate risk factors are present, including: first pregnancy, maternal age ≥35 years, BMI >30, family history of preeclampsia, or relevant sociodemographic/personal history factors. 1, 2
Antiphospholipid Antibody-Positive Without APS Criteria
For pregnant women with positive antiphospholipid antibodies who do NOT meet criteria for obstetric or thrombotic APS, prophylactic aspirin 81-100 mg daily is conditionally recommended as preeclampsia prophylaxis, starting before 16 weeks and continuing through delivery. 3 However, the combination of prophylactic heparin plus aspirin is conditionally recommended AGAINST in this population, unless individual high-risk circumstances exist (triple-positive aPL, strongly positive lupus anticoagulant, advanced maternal age, or IVF pregnancy). 3
Dosing and Timing
The standard dose is 81-100 mg daily. 3, 1, 2 While some investigators have used doses up to 150 mg daily, both the American College of Obstetricians and Gynecologists and U.S. Preventive Services Task Force note lack of comparative studies demonstrating superiority of higher doses. 3
Initiation must occur between 12-28 weeks of gestation, with optimal timing before 16 weeks, and continuation until delivery. 1, 2 Early initiation is critical for efficacy in preeclampsia prevention.
Safety Profile
Daily low-dose aspirin use in pregnancy is considered safe with low likelihood of serious maternal or fetal complications. 1, 2 The FDA label specifically warns against aspirin use during the last 3 months of pregnancy unless directed by a physician, as it may cause problems in the unborn child or complications during delivery. 4
Low-dose aspirin is not thought to complicate anesthesia or delivery, though decisions regarding discontinuation prior to delivery should be made by the obstetrician-gynecologist and anesthesiologist based on the patient's specific clinical situation. 3
Evidence for Efficacy
A Cochrane review demonstrated a 15% reduction in preeclampsia incidence and 7% reduction in deliveries before 37 weeks in high-risk populations, though overall fetal outcome improvement was modest and data remain conflicting. 3 Low-dose aspirin has proven efficacy for preventing preeclampsia and fetal growth restriction in high-risk patients, but benefits have NOT been demonstrated for vascular placental disease prevention in low-risk patients or for unexplained recurrent miscarriages. 5
What NOT to Use Aspirin For
In the absence of high-risk factors for preeclampsia, current evidence does not support prophylactic low-dose aspirin for prevention of early pregnancy loss, fetal growth restriction, stillbirth, or preterm birth. 1, 2
Critical Pitfalls to Avoid
Do not use aspirin as monotherapy in pregnant women with thrombotic APS—these patients require therapeutic-dose heparin (usually LMWH) plus low-dose aspirin throughout pregnancy and postpartum. 3
Do not add prednisone to standard aspirin plus heparin therapy in patients with refractory obstetric APS, as no controlled studies demonstrate benefit and potential risks are significant. 3
For ASA-sensitive pregnant women who require aspirin prophylaxis, aspirin desensitization is a valuable and safe therapeutic option that allows them to benefit from ASA's protective effects. 6
Do not prescribe aspirin for acute blood pressure management in preeclampsia—this is a prophylactic intervention only, not a treatment for active disease. 7, 8 The European Society of Cardiology specifically notes that diuretics should be avoided in preeclampsia as they further reduce plasma volume. 7