Emily Oster

7 min Read Emily Oster

Emily Oster

Low-Dose Aspirin in Pregnancy

Why all the new prescriptions?

Emily Oster

7 min Read

I’ve been getting a lot of questions about aspirin and pregnancy. These are not “Can I take aspirin for my headache?” but instead “My doctor prescribed a daily low-dose aspirin. Why?” In some cases, the reason given is COVID-related. A number of women told me they were prescribed a low-dose aspirin for the remainder of their pregnancy, either due to concerns about the placenta or a risk of blood clots. In other cases, this had nothing to do with COVID: other risk factors seemed to prompt the prescription.

This has been jarring for some, since many people recall a more traditional view that aspirin should not be taken during pregnancy, due to fear of bleeding. It remains true that typical adult doses of aspirin are not recommended for use as a painkiller. So why all the baby-aspirin prescriptions?

Low doses of aspirin are prescribed to lower the risk of preeclampsia, a condition that typically occurs near the end of pregnancy (or postpartum) and involves high blood pressure. It ranges from mild to extremely serious and affects about 6% of pregnancies in the U.S. Below, I’ll go through the data on the role of aspirin in lowering this risk and then talk about the targeting recommendations. I’ll return to COVID at the end.

Aspirin for preeclampsia

Daily aspirin treatment has been shown, based on multiple sizable randomized trials, to reduce the risk of preeclampsia. A 2019 Cochrane Review summarizes 72 randomized trials with almost 40,000 women. Treatment with aspirin (50 to 150 milligrams daily) reduces preeclampsia risk by about 20%. So if your baseline risk was 10%, this would reduce it to 8%. Treatment in these studies was generally started sometime between 12 and 16 weeks, and there isn’t much evidence to point to any particular dose being the right one. A common prescription is a “low dose” aspirin, which is 81 milligrams.

At times, concerns have been raised about the use of aspirin in pregnancy, specifically related to bleeding. However, the more recent updates have downgraded the evidence base for this risk, and the magnitude of any suggested effects are small. Longer-term follow-up on at least 5,000 children in these trials shows no developmental risks.

Bottom line: low-dose aspirin is a safe and effective method for preventing preeclampsia. As a result, it is standard to prescribe aspirin for women at high risk for preeclampsia. The question is, who is that?

Identifying risk groups

The U.S. Preventive Services Task Force recommends aspirin treatment for women at high risk of preeclampsia. It classifies high risk into two groups. First, some people are high-risk because of a single characteristic (e.g. previous preeclampsia, non-pregnancy hypertension), and some are high-risk because of a combination of several factors (e.g. obesity plus a family history of preeclampsia). I’ve put the full risk classification below.


These are all predictors that are observable before pregnancy. There are also markers of risk during pregnancy, including high levels of certain hormones. And of course, there is variation in risk even among people who are classified as high-risk by this simple criteria. The Fetal Medicine Foundation has a calculator for preeclampsia risk, based on both baseline characteristics and some medical measurements.

The one part of this risk categorization that is slightly complex is the last piece in the second column, the sociodemographic risk factors. Preeclampsia is more common in Black women than in non-Black women. However, it would be a mistake to think of race as a causal predictor; it is instead a marker of differential care and broader systemic inequality. As a consideration, though, it can be useful in making treatment decisions — and in ensuring that everyone gets the treatment they need — even if we absolutely agree it is not causal.

From an individual standpoint, you can use this list to figure out if you are a good candidate for treatment. In looking at it, it struck me as quite a large share of people. Anyone who is having their first child over 35. Anyone who is obese and over 35. Anyone who is Black and over 35, or having their first child. And so on.

To be a little more concrete, I loaded up the Natality Detail Files (I used 2018), which report information on all births in the U.S., including a lot of detail about mothers. Applying the criteria in the table above, I can estimate that — based on these pre-pregnancy characteristics alone — 28% of women would qualify as high-risk. Notably: there are other women who should qualify based on measurements taken during pregnancy.

There is a complicated question about where to draw the line of what risk level should qualify for treatment, for at least two reasons.

First: risk is a continuum, not a binary. Among those who would be classified as high-risk in the 2018 data, 11% developed preeclampsia, versus only 5.8% of those who would not have been classified this way. This suggests that the risk measure is predictive. However: within the “low risk” group, there is significant variation. For example, if we use “overweight” rather than “obese” as a risk factor, you identify an additional 10% of people as higher-risk. These intermediate-risk individuals have an 8% chance of developing preeclampsia, significantly higher than the 5.4% among the low-risk group. And, paradoxically, this group could end up being the highest-risk if you treat the “high risk” group with aspirin, significantly lowering their risk.

A second issue is that not everyone gets the same quality of prenatal care, and some women may not be identified as needing treatment because of missed diagnoses. Or they may not get the screening they need. Especially with these slightly complicated treatment guidelines, it’s easy for women to fall through the cracks.

Given the combination of the large share of women who should be treated with aspirin and the fact that there is little or no strong evidence of risk, some would make the case to routinely treat many more people. It is worse to undertreat than overtreat in this case, which could argue for a wider treatment range. I have heard it suggested that virtually everyone who is pregnant should be taking baby aspirin along with their folic acid in their prenatal vitamins. This isn’t the position of the American College of Obstetricians and Gynecologists (ACOG) or other official bodies, but it’s the logical extreme of a broader treatment tent.

In the end, I think this high-potential-benefit/low-risk factor may be the reason why we are seeing aspirin prescriptions for those who have recovered from COVID.

I cannot see any direct evidence linking aspirin use in pregnancy after COVID to better outcomes. Indeed, in talking to providers, reading the ACOG guidelines and scouring the medical literature, I am not entirely clear where this came from. It is true that we’ve seen compilations for pregnant people (especially unvaccinated people) who get COVID toward the end of pregnancy. And it’s true in some people COVID causes blood clots, and aspirin has been used to treat those. I can see how putting this together might lead one to conclude there is a benefit, but it’s quite indirect. Which I suspect is why we do not see ACOG or other organizations officially promoting this.

Having said that: there is much we still do not understand about COVID. It is possible that it affects the risk of preeclampsia, in which case aspirin would be very helpful. Under the broad treatment tent theory, it may be a good idea anyway, especially since the risks are very limited.

Thanks to Nate Fox for help on this one! And I hope at this point it goes without saying, but I am not a medical doctor, and you should definitely 1,000% talk with your doctor about any choices here before making them. Our goal is to arm you with data to make these conversations more productive.

Sep 19 2022

12 min read

Tylenol, Pregnancy, and That New Lawsuit

Why you shouldn't panic

Emily Oster
A close-up of a pregnant person holding a white pill and glass of water.

Jun 14 2021

7 min read

Tylenol in Pregnancy and ADHD

Unpacking a new paper

Emily Oster
Two pieces of yellow yarn are stretched across a blue background. The first piece is relatively straight, left to right. The second is tangled.

Jan 13 2023

2 min read

I Had Pregnancy Complications the First Time. Will They Happen for the Second Pregnancy?

I had severe nausea, fatigue, anxiety, and depression and preeclampsia (that one toward the end only) in my first pregnancy Read more

Emily Oster
Tylenol pills spill out of a bottle onto a peach background.

Apr 08 2022

2 min read

Can I Take Tylenol in the First Trimester?

About Tylenol in the first trimester if you get a cold or fever: What do I do this early (weeks Read more

Emily Oster

Instagram

left right
Looking for Memorial Day Weekend plans? Might be the perfect time to give potty training a shot. Potty training is notoriously difficult, and we unfortunately don’t have a lot of evidence-based guidance on what works best. So I asked the ParentData community to fill out a survey and share their knowledge — about 6,000 people responded.

👉Comment “Link” for a DM to an article that summarizes all of the best potty training advice we collected. 

Remember, you are not alone in the potty training struggle! It can be incredibly challenging, so please give yourself some grace.

#emilyoster #parentdata #pottytraining #pottytrainingtips #toddlertips

Looking for Memorial Day Weekend plans? Might be the perfect time to give potty training a shot. Potty training is notoriously difficult, and we unfortunately don’t have a lot of evidence-based guidance on what works best. So I asked the ParentData community to fill out a survey and share their knowledge — about 6,000 people responded.

👉Comment “Link” for a DM to an article that summarizes all of the best potty training advice we collected.

Remember, you are not alone in the potty training struggle! It can be incredibly challenging, so please give yourself some grace.

#emilyoster #parentdata #pottytraining #pottytrainingtips #toddlertips
...

We’re hiring an Associate Editor at ParentData! More details at my link in bio. Please share with the great writers and data-loving people in your network. 📊💻

We’re hiring an Associate Editor at ParentData! More details at my link in bio. Please share with the great writers and data-loving people in your network. 📊💻 ...

Do you brand things a certain way to get your kid to accept it? Like calling carrots “rabbit popsicles”? Or telling them to put on their “super speed socks” in the morning? Share your rebrands in the comments below! You never know who you might be helping out 👇

#emilyoster #funnytweets #relatabletweets #parentingjokes #kidssaythedarndestthings

Do you brand things a certain way to get your kid to accept it? Like calling carrots “rabbit popsicles”? Or telling them to put on their “super speed socks” in the morning? Share your rebrands in the comments below! You never know who you might be helping out 👇

#emilyoster #funnytweets #relatabletweets #parentingjokes #kidssaythedarndestthings
...

Have you ever panic-googled a parenting question when everyone else is asleep? If so, you’re not alone. 

Today is the first episode of a new biweekly series on my podcast: Late-Night Panic Google. On these mini-episodes, you’ll hear from some familiar names about the questions keeping them up at night, and how data can help. First up: @claireholt!

Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#parentdata #emilyoster #claireholt #parentingstruggles #parentingtips #latenightpanicgoogle

Have you ever panic-googled a parenting question when everyone else is asleep? If so, you’re not alone.

Today is the first episode of a new biweekly series on my podcast: Late-Night Panic Google. On these mini-episodes, you’ll hear from some familiar names about the questions keeping them up at night, and how data can help. First up: @claireholt!

Listen and subscribe to ParentData with Emily Oster in your favorite podcast app 🎧

#parentdata #emilyoster #claireholt #parentingstruggles #parentingtips #latenightpanicgoogle
...

Sun safety is a must for all ages, especially babies! Here are my tips for keeping your littlest ones protected in the sunshine:
☀️ Most importantly, limit their time out in hot weather. (They get hotter than you do!)
☀️ Keep them in the shade as much as possible when you’re out.
☀️ Long-sleeve but lightweight clothing is your friend, especially on the beach, where even in the shade you can get sunlight reflecting off different surfaces.
☀️ If you want to add a little sunscreen on their hands and feet? Go for it! But be mindful as baby skin tends to more prone to irritation.

Comment “Link” for a DM to an article on the data around sun and heat exposure for babies.

#sunsafety #babysunscreen #babyhealth #parentdata #emilyoster

Sun safety is a must for all ages, especially babies! Here are my tips for keeping your littlest ones protected in the sunshine:
☀️ Most importantly, limit their time out in hot weather. (They get hotter than you do!)
☀️ Keep them in the shade as much as possible when you’re out.
☀️ Long-sleeve but lightweight clothing is your friend, especially on the beach, where even in the shade you can get sunlight reflecting off different surfaces.
☀️ If you want to add a little sunscreen on their hands and feet? Go for it! But be mindful as baby skin tends to more prone to irritation.

Comment “Link” for a DM to an article on the data around sun and heat exposure for babies.

#sunsafety #babysunscreen #babyhealth #parentdata #emilyoster
...

I’m calling on you today to share your story. I know that many of you have experienced complications during pregnancy, birth, or postpartum. It’s not something we want to talk about, but it’s important that we do. Not just for awareness, but to help people going through it feel a little less alone.

That’s why I’m asking you to post a story, photo, or reel this week with #MyUnexpectedStory and tag me. I’ll re-share as many as I can to amplify. Let’s fill our feeds with these important stories and lift each other up. Our voices can create change. And your story matters. 💙

#theunexpected #emilyoster #pregnancycomplications #pregnancystory

I’m calling on you today to share your story. I know that many of you have experienced complications during pregnancy, birth, or postpartum. It’s not something we want to talk about, but it’s important that we do. Not just for awareness, but to help people going through it feel a little less alone.

That’s why I’m asking you to post a story, photo, or reel this week with #MyUnexpectedStory and tag me. I’ll re-share as many as I can to amplify. Let’s fill our feeds with these important stories and lift each other up. Our voices can create change. And your story matters. 💙

#theunexpected #emilyoster #pregnancycomplications #pregnancystory
...

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio!

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio! ...

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio!

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio! ...

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio!

OUT NOW: My new book “The Unexpected: Navigating Pregnancy During and After Complications” is available on April 30th. All of my other books came out of my own experiences. I wrote them to answer questions I had, as a pregnant woman and then as a new parent. “The Unexpected” is a book not to answer my own questions but to answer yours. Specifically, to answer the thousands of questions I’ve gotten over the past decade from people whose pregnancies were more complicated than they had expected. This is for you. 💛 Order now at my link in bio! ...

Is side sleeping important during pregnancy? Comment “Link” for a DM to an article on whether sleep position affects pregnancy outcomes.

Being pregnant makes you tired, and as time goes by, it gets increasingly hard to get comfortable. You were probably instructed to sleep on your side and not your back, but it turns out that advice is not based on very good data.

We now have much better data on this, and the bulk of the evidence seems to reject the link between sleep position and stillbirth or other negative outcomes. So go ahead and get some sleep however you are most comfortable. 💤

Sources:
📖 #ExpectingBetter pp. 160-163
📈 Robert M. Silver et al., “Prospective Evaluation of Maternal Sleep Position Through 30 Weeks of Gestation and Adverse Pregnancy Outcomes,” Obstetrics and Gynecology 134, no. 4 (2019): 667–76. 

#emilyoster #pregnancy #pregnancytips #sleepingposition #pregnantlife

Is side sleeping important during pregnancy? Comment “Link” for a DM to an article on whether sleep position affects pregnancy outcomes.

Being pregnant makes you tired, and as time goes by, it gets increasingly hard to get comfortable. You were probably instructed to sleep on your side and not your back, but it turns out that advice is not based on very good data.

We now have much better data on this, and the bulk of the evidence seems to reject the link between sleep position and stillbirth or other negative outcomes. So go ahead and get some sleep however you are most comfortable. 💤

Sources:
📖 #ExpectingBetter pp. 160-163
📈 Robert M. Silver et al., “Prospective Evaluation of Maternal Sleep Position Through 30 Weeks of Gestation and Adverse Pregnancy Outcomes,” Obstetrics and Gynecology 134, no. 4 (2019): 667–76.

#emilyoster #pregnancy #pregnancytips #sleepingposition #pregnantlife
...

My new book, “The Unexpected: Navigating Pregnancy During and After Complications” is available for preorder at the link in my bio!

I co-wrote #TheUnexpected with my friend and maternal fetal medicine specialist, Dr. Nathan Fox. The unfortunate reality is that about half of pregnancies include complications such as preeclampsia, miscarriage, preterm birth, and postpartum depression. Because these are things not talked about enough, it can not only be an isolating experience, but it can also make treatment harder to access.

The book lays out the data on recurrence and delves into treatment options shown to lower risk for these conditions in subsequent pregnancies. It also guides you through how to have productive conversations and make shared decisions with your doctor. I hope none of you need this book, but if you do, it’ll be here for you 💛

#pregnancy #pregnancycomplications #pregnancyjourney #preeclampsiaawareness #postpartumjourney #emilyoster

My new book, “The Unexpected: Navigating Pregnancy During and After Complications” is available for preorder at the link in my bio!

I co-wrote #TheUnexpected with my friend and maternal fetal medicine specialist, Dr. Nathan Fox. The unfortunate reality is that about half of pregnancies include complications such as preeclampsia, miscarriage, preterm birth, and postpartum depression. Because these are things not talked about enough, it can not only be an isolating experience, but it can also make treatment harder to access.

The book lays out the data on recurrence and delves into treatment options shown to lower risk for these conditions in subsequent pregnancies. It also guides you through how to have productive conversations and make shared decisions with your doctor. I hope none of you need this book, but if you do, it’ll be here for you 💛

#pregnancy #pregnancycomplications #pregnancyjourney #preeclampsiaawareness #postpartumjourney #emilyoster
...

We are better writers than influencers, I promise. Thanks to our kids for filming our unboxing videos. People make this look way too easy. 

Only two weeks until our book “The Unexpected” is here! Preorder at the link in my bio. 💙

We are better writers than influencers, I promise. Thanks to our kids for filming our unboxing videos. People make this look way too easy.

Only two weeks until our book “The Unexpected” is here! Preorder at the link in my bio. 💙
...

Exciting news! We have new, high-quality data that says it’s safe to take Tylenol during pregnancy and there is no link between Tylenol exposure and neurodevelopmental issues in kids. Comment “Link” for a DM to an article exploring this groundbreaking study.

While doctors have long said Tylenol was safe, confusing studies, panic headlines, and even a lawsuit have continually stoked fears in parents. As a result, many pregnant women have chosen not to take it, even if it would help them.

This is why good data is so important! When we can trust the data, we can trust our choices. And this study shows there is no blame to be placed on pregnant women here. So if you have a migraine or fever, please take your Tylenol.

#tylenol #pregnancy #pregnancyhealth #pregnancytips #parentdata #emilyoster

Exciting news! We have new, high-quality data that says it’s safe to take Tylenol during pregnancy and there is no link between Tylenol exposure and neurodevelopmental issues in kids. Comment “Link” for a DM to an article exploring this groundbreaking study.

While doctors have long said Tylenol was safe, confusing studies, panic headlines, and even a lawsuit have continually stoked fears in parents. As a result, many pregnant women have chosen not to take it, even if it would help them.

This is why good data is so important! When we can trust the data, we can trust our choices. And this study shows there is no blame to be placed on pregnant women here. So if you have a migraine or fever, please take your Tylenol.

#tylenol #pregnancy #pregnancyhealth #pregnancytips #parentdata #emilyoster
...