Pregnancy

Low-Dose Aspirin: Preventing Preeclampsia

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Low-dose aspirin is recommended in some pregnancies to help prevent preeclampsia, a dangerous rise in blood pressure. For people at high risk, a daily 81 mg dose started before 16 weeks lowers the odds of preterm preeclampsia by about 60%, according to ACOG and major trials. It is not needed in low-risk pregnancies.

Last updated: July 2026History

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What is preeclampsia, and why does aspirin help?

Preeclampsia is a pregnancy complication marked by high blood pressure and signs of organ stress, usually appearing after 20 weeks 4. Aspirin appears to help by improving how the placenta's blood vessels form early in pregnancy, and its antiplatelet effect reduces the abnormal clotting and inflammation that drive the disorder. According to ACOG, low-dose aspirin lowers the chance of preeclampsia and its complications, including preterm birth and restricted fetal growth 13.

The medicine does not treat preeclampsia once it has developed; its role is purely prevention. That is why timing matters so much. Starting between 12 and 28 weeks, and ideally before 16 weeks, gives the placenta the window in which aspirin can still shape vessel development 1. Knowing the preeclampsia symptoms to watch for is a useful companion to prevention.

Who is advised to take low-dose aspirin?

Low-dose aspirin is targeted at pregnancies with a meaningfully higher preeclampsia risk, not offered to everyone. ACOG and national guidance list high-risk factors, including a prior pregnancy with preeclampsia, chronic high blood pressure, type 1 or type 2 diabetes, kidney disease, autoimmune conditions such as lupus, or carrying more than one baby, where daily aspirin is recommended 1.

Moderate-risk factors, such as a first pregnancy, obesity, a family history of preeclampsia, being 35 or older, or a gap of more than 10 years since a last pregnancy, may justify aspirin when several stack together 1. People with none of these usually gain little, because their baseline risk is already low. A clinician weighs your blood-pressure history and full picture before deciding.

How strong is the evidence behind it?

Large trials and pooled analyses give aspirin one of the better evidence bases in obstetric prevention. The ASPRE trial randomized high-risk women and found that aspirin cut preterm preeclampsia by about 62% compared with placebo 2. A Cochrane review of antiplatelet agents, drawing on tens of thousands of participants, reported roughly a 15 to 18% reduction in preeclampsia overall, with fewer preterm births and fewer pregnancies lost 3.

According to this guideline-level evidence, the benefit is real but modest in absolute terms: meaningful for someone at high risk, and negligible for someone at low risk. Society recommendations reflect that trade-off by reserving aspirin for the pregnancies most likely to gain 1. That targeting is what keeps the benefit worthwhile against any small downside.

Is low-dose aspirin safe for the baby?

Low-dose aspirin has a reassuring safety record in pregnancy at the amounts used for preeclampsia prevention. Studies have not found an increase in bleeding problems, birth defects, or placental abruption at the 81 mg level 1. Higher, pain-relief doses are a different matter and are generally avoided, especially late in pregnancy, because full-dose anti-inflammatory drugs can affect the baby's circulation.

The low dose also carries a longer thread across life stages. A history of preeclampsia signals roughly double the later risk of high blood pressure and heart disease as a woman moves into midlife, so preventing it may matter well beyond delivery, according to the American Heart Association 5. Mild stomach upset is the most common side effect, and pairing the tablet with food often eases it.

When aspirin questions need an obstetrician

Deciding whether low-dose aspirin fits your pregnancy is a clinical judgment, not a self-serve choice. An obstetrician or the clinician managing your prenatal care can score your risk factors, confirm the timing, and check for reasons to avoid aspirin, such as a bleeding disorder or an aspirin allergy.

Because the window before 16 weeks matters most, this conversation ideally happens early, often at your first prenatal visit or while planning a pregnancy. Bringing your history of high blood pressure, prior pregnancies, and your current prenatal vitamins helps that discussion move quickly. Gale can help you prepare for that conversation.

Common questions

It is the same drug at a smaller amount. The low dose used in pregnancy is 81 mg, versus the 325 mg strength common in adult pain-relief tablets. The 81 mg dose is what the preeclampsia-prevention studies used.

Guidance points to starting between 12 and 28 weeks, ideally before 16 weeks, and continuing until close to delivery or as a clinician advises. The exact timing is set by your care team based on your risk factors.

Studies at the 81 mg level have not shown increased miscarriage, bleeding, or birth defects. The doses generally avoided later in pregnancy are the higher, full-strength anti-inflammatory doses, not low-dose aspirin.

A single missed low dose is not an emergency. Consistency across the pregnancy matters more than any one tablet, and your clinician can advise on how to get back on track if you forget.

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Preeclampsia warning signs that need prompt care

  • —A severe or persistent headache that does not ease with rest is a reason to contact your obstetric team the same day.
  • —New vision changes such as blurring, flashing lights, or spots after 20 weeks are a reason to seek urgent clinician review.
  • —Sudden swelling of the face or hands with upper-abdominal pain is a reason to be evaluated right away.
  • —Any vaginal bleeding while taking low-dose aspirin is a reason to check in with your clinician promptly.

Severe headache, vision changes, or upper-abdominal pain in the second half of pregnancy can signal preeclampsia. Call your obstetric provider immediately or go to labor and delivery or the nearest emergency room.

This article is general health education, not medical advice. Whether low-dose aspirin is right for your pregnancy is a decision for an obstetrician or the clinician managing your prenatal care.

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References

  1. 1.American College of Obstetricians and Gynecologists (2018). ACOG Committee Opinion No. 743: Low-Dose Aspirin Use During Pregnancy. Obstetrics & Gynecology. doi:10.1097/AOG.0000000000002708 ✓ACOG guidance recommending low-dose 81 mg aspirin for pregnancies at high preeclampsia risk, the high- and moderate-risk factor lists, initiation between 12 and 28 weeks (ideally before 16 weeks), and its favorable low-dose safety profile.
  2. 2.Rolnik DL, Wright D, Poon LC, et al. (2017). Aspirin versus placebo in pregnancies at high risk for preterm preeclampsia. New England Journal of Medicine. doi:10.1056/NEJMoa1704559 ✓The ASPRE randomized trial showing aspirin reduced preterm preeclampsia by about 62% versus placebo in high-risk pregnancies.
  3. 3.Duley L, Meher S, Hunter KE, Seidler AL, Askie LM (2019). Antiplatelet agents for preventing pre-eclampsia and its complications. Cochrane Database of Systematic Reviews. doi:10.1002/14651858.CD004659.pub3 ✓Cochrane meta-analysis of antiplatelet agents finding roughly a 15 to 18% reduction in preeclampsia with fewer preterm births and fewer pregnancy losses.
  4. 4.American College of Obstetricians and Gynecologists (2020). Gestational Hypertension and Preeclampsia: ACOG Practice Bulletin, Number 222. Obstetrics & Gynecology. doi:10.1097/AOG.0000000000003891 ✓ACOG definition of preeclampsia as new high blood pressure and organ-stress signs, typically after 20 weeks of pregnancy.
  5. 5.Parikh NI, et al. (American Heart Association) (2021). Adverse Pregnancy Outcomes and Cardiovascular Disease Risk: Unique Opportunities for Cardiovascular Disease Prevention in Women: A Scientific Statement From the American Heart Association. Circulation. doi:10.1161/CIR.0000000000000961 ✓AHA scientific statement linking a history of preeclampsia to elevated later-life cardiovascular disease and hypertension risk in women.

5 sources, numbered by first appearance. General health information, not medical advice. AI-assisted editorial content — every citation independently verified. Editorial policy

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