Is Low-Dose aspirin safe during pregnancy?

What does the evidence say about Low-Dose aspirin during pregnancy?

1. The usual pregnancy dose is 81 mg a day, within a low-dose range generally defined as 60 to 150 mg. 1
2. Providers prescribe low-dose aspirin for a history of pregnancy loss or a higher chance of preeclampsia, and it's thought to work partly by improving blood flow to the placenta and calming inflammation. 1
3. Preeclampsia is a high blood pressure disorder linked to reduced blood flow to the placenta, the same pathway low-dose aspirin is thought to affect. 2
4. Taking low-dose aspirin exactly as your provider directs is not expected to raise the chance of miscarriage and hasn't been linked to a higher chance of birth defects, but it should only be used under a provider's care. 1
5. Full-strength aspirin taken without provider guidance is a different story: it's been linked to a higher chance of miscarriage around the time of conception, a possible signal for the birth defect gastroschisis in a few small studies, and later-pregnancy concerns like bleeding and reduced amniotic fluid. 3

Is Low-Dose aspirin safe in each trimester?

• First trimester. If you have risk factors linked to a higher chance of preeclampsia, like chronic high blood pressure, a past preeclampsia pregnancy, carrying multiples, certain autoimmune or kidney conditions, or conceiving through assisted reproduction, your provider may start you on daily low-dose aspirin early on. This is always a decision made with your provider, not something to start on your own. The usual dose is 81 mg a day: don't swap in a 325 mg tablet or stack extra pills to reach that number without your provider confirming the exact product and dose.
• Second trimester. If you already started low-dose aspirin, keep taking it every day through the second trimester. The benefit comes from steady daily use, not occasional dosing. Taken as your provider directs, it hasn't been linked to a higher chance of miscarriage or birth defects. If you weren't flagged as a candidate earlier, ask your provider at a routine visit whether anything about your risk profile has changed.
• Third trimester. Most people continue the same 81 mg daily dose through the third trimester and up to delivery, since stopping early would undo the benefit your provider is aiming for. Full-strength aspirin is a different matter here: taken without supervision, especially after 20 weeks, it's been linked to bleeding, reduced amniotic fluid, and effects on the baby's heart. Only your obstetric provider should decide whether or when to adjust your aspirin plan as delivery gets closer.