Preeclampsia is a serious pregnancy complication characterized by high blood pressure and signs of damage to another organ system, often the kidneys. For decades, researchers have explored ways to prevent this condition, and low-dose aspirin has emerged as a key preventative measure for women at high risk. But Why Do Doctors Prescribe Aspirin During Pregnancy, especially when it’s generally avoided in other contexts of pregnancy? The answer lies in aspirin’s potential to address the underlying causes of preeclampsia and the compelling evidence supporting its benefits for certain pregnant individuals.
Understanding the Link Between Aspirin and Preeclampsia
The initial rationale for using aspirin to prevent preeclampsia stemmed from the hypothesis that the condition is linked to imbalances in certain substances in the blood vessels. Specifically, researchers focused on prostacyclin and thromboxane A2 (TXA2). Prostacyclin helps to widen blood vessels and prevent blood clots, while TXA2 does the opposite, narrowing blood vessels and promoting clotting. An imbalance, with too much TXA2 and not enough prostacyclin, could lead to vascular issues and coagulation problems thought to be involved in preeclampsia.
Low-dose aspirin is known to affect these substances. It preferentially inhibits TXA2 production, thus potentially restoring a better balance between prostacyclin and TXA2. This theoretical benefit led to early investigations into aspirin’s role in preeclampsia prevention.
Evidence Supporting Aspirin for Preeclampsia Prevention
Initial small studies suggested that low-dose aspirin could indeed be beneficial for women at high risk of preeclampsia. However, larger, more definitive Randomized Controlled Trials (RCTs) were needed to confirm these findings. One significant study, the 2017 Aspirin for Evidence-Based Preeclampsia Prevention (ASPRE) trial, provided strong evidence. This trial randomized women identified as high-risk for preeclampsia in the first trimester to either 150mg of aspirin or a placebo. The results showed a significant reduction in preterm preeclampsia – cases occurring before 37 weeks of gestation – in the aspirin group.
Furthermore, meta-analyses, which combine data from multiple studies to provide a more robust conclusion, have also supported the use of low-dose aspirin. A meta-analysis of individual patient data from 31 RCTs indicated a modest but significant reduction in preeclampsia risk with low-dose aspirin. A Cochrane review, analyzing data from 59 trials, reported a 17% relative reduction in preeclampsia. While some caution is advised in interpreting the magnitude of risk reduction due to potential publication bias, the overall trend from numerous studies points towards a protective effect of low-dose aspirin.
The United States Preventive Services Task Force (USPSTF) also conducted a systematic review of high-quality RCTs. Their 2014 guideline concluded that low-dose aspirin (60-150 mg/day) demonstrated a 24% reduction in preeclampsia in women at high risk. Although they suggested the actual reduction might be closer to 10% due to “small study effects”, the evidence was strong enough to recommend its use in specific populations.
Who Should Consider Aspirin During Pregnancy?
Based on the accumulated evidence and guidelines from organizations like USPSTF, the American College of Obstetricians and Gynecologists (ACOG), and the Society for Maternal-Fetal Medicine (SMFM), low-dose aspirin (81 mg/day) is recommended for women identified as being at high risk of preeclampsia.
Risk factors that categorize a woman as high-risk include:
- History of preeclampsia, especially preterm preeclampsia.
- Multifetal gestation (twins, triplets, etc.).
- Chronic hypertension.
- Pre-existing diabetes (type 1 or type 2).
- Kidney disease.
- Autoimmune diseases such as systemic lupus erythematosus or antiphospholipid syndrome.
Women with multiple moderate risk factors are also considered for low-dose aspirin prophylaxis. These moderate risk factors can include:
- First pregnancy.
- Obesity (BMI > 30 kg/m²).
- Family history of preeclampsia (mother or sister).
- Socioeconomic factors.
- Age 35 years or older.
- Adverse pregnancy outcome in a previous pregnancy.
- Interval between pregnancies of more than 10 years.
Risk assessment is typically performed by healthcare providers, often starting in the first trimester. Some screening algorithms also incorporate first-trimester serum markers and uterine artery Doppler studies to refine risk prediction, although the generalizability of these algorithms might vary across populations.
Dosage and Timing of Aspirin
The recommended dose of aspirin for preeclampsia prevention is low-dose, specifically 81 mg per day. It is generally advised to start aspirin between 12 and 28 weeks of gestation, ideally before 16 weeks. Daily use should continue until delivery. For women already taking low-dose aspirin for other medical reasons before pregnancy, continuation of aspirin treatment is generally advised.
Conclusion: Aspirin as a Preventative Measure
In conclusion, doctors prescribe low-dose aspirin during pregnancy for women at increased risk of preeclampsia because robust scientific evidence indicates it modestly reduces this risk. Major medical organizations support this recommendation, highlighting the favorable balance of benefits and minimal risks associated with low-dose aspirin in this context. By understanding the link between aspirin and preeclampsia, and by identifying high-risk individuals, healthcare providers can effectively utilize low-dose aspirin as a preventative strategy to improve maternal and fetal outcomes.
