What’s the Data Behind Baby Aspirin Recommendations?

Have the dosage recommendations changed for baby aspirin? I’m high-risk for preeclampsia, and my doctor initially told me to take 81mg and recently upped that dose to 162mg. This seems like a big jump.

—Anonymous

Low-dose aspirin (sometimes called “baby” aspirin) has been shown to reduce the risk of preeclampsia by about 10-20%. It is important to note that this reduction is a relative reduction, meaning if your risk of developing preeclampsia was 20% at baseline, a relative reduction of 10-20% would mean your risk lowers to 16-18%, not to 0%.

Because of this, low-dose aspirin is recommended to a wide variety of patients who could be at increased risk of developing preeclampsia, like those previously diagnosed with it in a prior pregnancy. Other reasons include having certain medical conditions like chronic hypertension, diabetes, and twin pregnancies. However, studies have shown a reduction in all patients who take low-dose aspirin, so different people have different thresholds for when they recommend low-dose aspirin. For example, in my practice, we generally recommend it to all patients unless there is a good reason not to. Low-dose aspirin is typically started around the end of the first trimester, as this is when it is most effective in preventing preeclampsia later in pregnancy — it will not treat preeclampsia once one has it.

In terms of your question about the optimal dose, we don’t (yet) have a great answer to that. In the many studies that have looked at low-dose aspirin to prevent preeclampsia, a wide range of doses have been studied, ranging from 75mg to 150mg, and no single dose has been shown to be better than another or if certain doses are most appropriate for certain risk factors (a higher dose for a higher risk, for example). Some data suggest that a higher dose is more effective, but there has not been a large, randomized trial comparing two doses to determine the better dose.

In practice, in the U.S., most doctors recommend 81mg because that is the dose that is commercially available. Around the world, many recommend 100mg or 150mg because those dosing formulations are more common in other countries.

In my practice, I typically recommend 81mg. However, for certain very high-risk patients, I may recommend taking two low-dose aspirin (162mg), which isn’t a far cry from the 150mg used in many studies and is a pragmatic way for someone to take a higher dose. Perhaps that is what your doctor was thinking as well.