General Advice on Aspirin in Pregnancy
Pregnant women are not universally advised against aspirin, but recommendations depend on dose, trimester, and medical need. Low-dose aspirin (81 mg daily) is often recommended for high-risk pregnancies to prevent preeclampsia, starting around 12 weeks.[1][2] Higher doses (325 mg or more) are generally avoided, especially in the third trimester, due to risks like bleeding and premature closure of the fetal ductus arteriosus.[3]
When Low-Dose Aspirin Is Recommended
The U.S. Preventive Services Task Force (USPSTF) advises low-dose aspirin for women at high risk of preeclampsia, such as those with chronic hypertension, type 2 diabetes, or prior preeclampsia. ACOG and SMFM endorse this from 12 weeks until delivery, reducing preeclampsia risk by 24% and fetal growth restriction by 14% in trials.[1][4] It's safe when prescribed; studies show no increased birth defect risk.[2]
Risks with Higher Doses or Late Pregnancy
Full-dose aspirin inhibits prostaglandins, raising concerns for:
- Third-trimester use: Fetal ductus arteriosus closure, leading to pulmonary hypertension (avoid after 30 weeks).[3][5]
- Near delivery: Increased maternal/fetal bleeding.[3]
- First trimester: Possible miscarriage or congenital defects with high doses, though evidence is mixed for low doses.[6]
The FDA labels aspirin Pregnancy Category D in third trimester (positive evidence of risk).[5]
Differences by Trimester
| Trimester | Low-Dose (81 mg) | High-Dose (≥325 mg) |
|-----------|------------------|---------------------|
| First | Generally safe; some data suggest slight miscarriage risk, but not conclusive | Avoid; potential cardiac defects |
| Second | Recommended for preeclampsia prevention | Use only if benefits outweigh risks (e.g., arthritis) |
| Third | Continue until delivery for indicated cases | Contraindicated due to bleeding/ductus risks |
What Happens If Taken Without Advice?
Overuse can cause fetal kidney issues or oligohydramnios. Always consult an OB-GYN; self-medication is discouraged.[3][7] No evidence supports routine aspirin for all pregnancies.
Alternatives for Pain or Prevention