If you’re pregnant, you’ve probably been told to avoid taking most pain medications. But there’s one notable exception to this rule: Some moms-to-be — including those with certain high-risk pregnancies — may want to start taking a low dose of aspirin every day beginning in their third or fourth month of pregnancy.
Research shows that taking low-dose aspirin (also known as “baby aspirin”) during pregnancy can help prevent preeclampsia — a pregnancy-related high blood pressure disorder that affects up to 8% of pregnancies and is responsible for causing some harmful complications, according to the March of Dimes.[1]
While preeclampsia is diagnosed after week 20 of pregnancy but before week 32, it’s thought that taking baby aspirin early on — before week 16, for example — can help ward off some of the potential complications of the condition.
"Every person should be screened for preeclampsia early in their pregnancy," says Beth McGovern, D.N.P., R.N.C.-O.B., a spokeswoman for the March of Dimes and its Low Dose, Big Benefits campaign. "Patients should request a screening at their first prenatal care visit … and discuss with their provider whether low-dose aspirin is right for them."
Here’s what you should know about low-dose aspirin, including who might benefit the most.
What is baby aspirin?
Aspirin is a type of medication that helps bring down fever, pain, and swelling, and prevent blood clots.
In its regular-strength form — i.e., a 325-milligram dose — it’s given to ease symptoms like headaches, muscle aches, and joint pain. In lower doses, it can be given to help prevent preeclampsia during pregnancy.
In the United States, low-dose aspirin usually comes in 81-milligram form (hence its nickname, “baby aspirin”), although amounts ranging from 60 to 150 milligrams are also considered low-dose.
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What are the benefits of taking baby aspirin during pregnancy?
Studies have shown that taking baby aspirin, ideally before 16 weeks of pregnancy, can lower the risk of preeclampsia — a type of pregnancy-induced high blood pressure that can cause complications like HELLP syndrome and preterm delivery. (Preeclampsia is defined as blood pressure that’s higher than 140/90 mm Hg and accompanied by protein in the urine.)
It's especially helpful in warding off "preterm preeclampsia," the kind that occurs before 32 weeks of pregnancy, says Shannon Smith, M.D., a board-certified OB/GYN at Brigham Faulkner OB/GYN Associates in Boston, Massachusetts, and a member of the What to Expect Medical Review Board.
"Studies show that low dose aspirin does not change the incidence of term preeclampsia, but decreases the incidence of preterm preeclampsia — especially at less than 32 weeks gestation," Dr. Smith notes. "So that is the main goal. And by decreasing the incidence preterm, the complications of preterm delivery are also avoided in the newborn."
Babies who are born prematurely can have a higher risk of health problems, such as newborn jaundice and hearing or vision problems. And preeclampsia can be harmful to the mother too.
“Preeclampsia is associated with a higher risk of maternal death as well as preterm birth,” says Naima Joseph, M.D., a maternal fetal medicine specialist at Boston University School of Medicine, in Boston, Massachusetts.
Preeclampsia is thought to develop in part when the placenta abnormally implants in the body, where it can then cause chronic inflammation that can lead to complications, including high blood pressure. It can also harm the kidneys, liver, and other organs in the mother, according to the March of Dimes.
“Low-dose aspirin reduces preeclampsia by inhibiting some of the inflammation that occurs at the placental level,” says Dr. Joseph.
Studies show that taking low-dose aspirin to lower the risk of preeclampsia (or delay it as much as possible) can also help prevent preeclampsia-related complications, including preterm birth and intrauterine growth restriction (IUGR). [2]
“If you never develop preeclampsia, you’re less likely to have a preterm birth, and you’re less likely to have a baby that’s in the NICU,” says McGovern.
Who should take baby aspirin during pregnancy?
Your doctor may recommend a course of low-dose aspirin if you have a high risk for preeclampsia. Pregnant women who are at high risk of the condition include those with at least one of the following risk factors:
A history of preeclampsia
Hypertension, kidney disease, or an autoimmune disease such as lupus.
Pre-existing type 1 or type 2 diabetes
You may also be a candidate for low-dose aspirin if you have a moderate risk of preeclampsia, which includes more than one of the following risk factors:
Obesity
A family history of preeclampsia
Black race (i.e., associated with systemic racism, which is associated with environmental and medical inequalities)
Lower income
Age 35 or older
Having in vitro fertilization (IVF)
A history of low-birth-weight babies or babies born small for their gestational age
A history of adverse pregnancy outcomes
A history of miscarriage or stillbirth
Are there any risks of taking baby aspirin during pregnancy?
If you’re allergic to aspirin or other salicylate medications, you may not be a candidate for low-dose aspirin. Otherwise, research shows that taking baby aspirin during pregnancy is safe.
“There’s very little downside to taking it,” says Cynthia Gyamfi-Bannerman, MD, department chair and maternal fetal medicine specialist at U.C. San Diego Health who co-authored the committee opinion on baby aspirin and pregnancy for the American College of Obstetricians and Gynecologists (ACOG).[3]
There’s a small concern that taking aspirin can slightly increase the risk of bleeding, but there are a lot of studies that suggest there is no evidence of an increase in bleeding during or after delivery, says Dr. Gyamfi-Bannerman.
Even though there aren’t many risks of taking low-dose aspirin during pregnancy, you should always get the green light from your doctor before taking that or any other medication during pregnancy.
When should you start taking baby aspirin during pregnancy?
For pregnant women who are at risk of preeclampsia, ACOG recommends taking a low dose of aspirin between 12 and 28 weeks, but some studies show that it’s best to start taking it before 16 weeks.
For example, one research review published in the American Journal of Obstetrics and Gynecology found that when pregnant women started taking aspirin at or before 16 weeks, the medication was more effective at preventing preeclampsia and fetal growth restriction than when it was started after 16 weeks.[4]
“We really want people to start taking low-dose aspirin around that 12-to-16-week mark because that’s when the placenta is developing at a fast rate and there's a lot of fetal growth,” says McGovern.
In all likelihood, that means either you or your doctor will bring up the subject of whether you’re a candidate for low-dose aspirin at your first or second prenatal appointment, around week 8 or week 12, depending on when you see your provider.
"I usually see people at a 10-week visit," says Dr. Smith. "I use this visit to counsel on the benefits of adding a baby aspirin to their daily regimen in the next few weeks — most of my patients meet criteria, so it has become very routine now."
Still, even if you start taking aspirin after 16 weeks, there may be some benefit to taking the medication.
“When you think about who bears the highest burden of preeclampsia, we know that it’s in people of color and people from low-resource settings who may not present to pregnancy care until 20 weeks,” says Dr. Joseph. “Because of that, there may be [at least a little] benefit to starting aspirin, even that late in pregnancy.”
Starting a low-dose aspirin regimen after 28 weeks, however, may be too late to prevent preeclampsia from developing, says Dr. Gyamfi-Bannerman.
When is the best time of day to take low-dose aspirin?
There’s no best time to take baby aspirin, but some experts recommend taking it at the same time as your prenatal vitamins, mainly so you remember it. Regardless, you should take low-dose aspirin with a glass of water.
Does baby aspirin have any side effects during pregnancy?
There are some possible side effects of low-dose aspirin, including:
Gastrointestinal bleeding or stomach ulcers among people who are taking aspirin every day.
Trouble breathing among people who have nasal polyps (or soft growths on the lining of the nose or sinuses).
Allergic reactions, including anaphylaxis, among people who are allergic to aspirin.
“For the majority of people, aspirin is very safe and very tolerable,” says Dr. Joseph.
When should you stop taking low-dose aspirin?
Your doctor will likely recommend taking low-dose aspirin until you give birth. In some studies conducted outside the U.S., researchers stopped giving pregnant women aspirin at 36 weeks because they worried about the possibility of bleeding, but ACOG recommends taking aspirin up until delivery.
While preeclampsia can also appear after you give birth, there’s no evidence that low-dose aspirin can help ward off postpartum preeclampsia too.
Aspirin helps tamp down some of the inflammation at the placenta level, says Dr. Joseph, but once the placenta is no longer in the body, there may not be any benefits to taking the aspirin.
If you’re taking low-dose aspirin for another condition, it should be safe to breastfeed while on the medication. Small amounts of aspirin can enter breast milk, but research hasn't found any negative effects in babies.
”There have been numerous research studies done all the way up to children in elementary school on moms who took low-dose aspirin, and there are really no negative side effects to the fetus,” says McGovern.
You should avoid taking regular-strength aspirin (325 mg), though, because there are possible risks to the baby, including hemolysis (damage to red blood cells) and a theoretical risk of Reye syndrome (a brain disease), says Dr. Smith.
Timing is key, so always talk to your doctor before starting — or stopping — a low-dose aspirin regimen. Once you get the green light, though, taking baby aspirin correctly means that you can boost your odds of having a healthy pregnancy.
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