Ibuprofen can harm a developing baby in several ways depending on when during pregnancy you take it. In the first trimester, it may raise the risk of miscarriage. From 20 weeks onward, it can damage the baby’s kidneys and reduce amniotic fluid, sometimes in as little as 48 hours. In the third trimester, it can cause a critical blood vessel in the baby’s heart to close too early. The FDA issued a formal warning in 2020 recommending against all NSAID use after 20 weeks of pregnancy, and the American College of Obstetricians and Gynecologists (ACOG) considers acetaminophen the safest pain reliever during pregnancy instead.
First Trimester: Possible Miscarriage Risk
The safety of ibuprofen in early pregnancy isn’t fully established. Some studies suggest it may increase the chance of miscarriage, particularly when taken around the time of conception or over an extended period. The challenge is that miscarriages are common and have many potential causes, making it difficult to isolate whether a medication, an underlying health condition, or something else is responsible. Because of this uncertainty, ACOG notes that it’s “not clear if ibuprofen and naproxen are safe for a fetus during the first trimester.”
After 20 Weeks: Kidney Problems and Low Amniotic Fluid
This is where the risks become more concrete. After about 20 weeks, the baby’s kidneys take over as the primary source of amniotic fluid. Ibuprofen and other NSAIDs can impair those developing kidneys, reducing how much fluid they produce. Amniotic fluid cushions the baby, supports lung development, and allows movement. When levels drop too low, it can lead to serious complications.
The FDA reviewed published case reports and found that low amniotic fluid levels appeared after NSAID use lasting anywhere from 48 hours to several weeks. On average, the problem showed up after days to weeks of treatment, but in some cases it developed in just two days. The good news is that in most reported cases, the low fluid levels improved after the NSAID was stopped. But the potential for harm is real enough that the FDA now recommends avoiding all NSAIDs from week 20 onward.
Third Trimester: A Blood Vessel That Closes Too Soon
Before birth, babies have a small blood vessel called the ductus arteriosus that reroutes blood away from the lungs (since they aren’t breathing air yet). This vessel stays open thanks to prostaglandins, hormone-like chemicals that ibuprofen is specifically designed to block. When you take ibuprofen late in pregnancy, it can cause this vessel to constrict or close prematurely.
If the ductus arteriosus narrows before delivery, blood gets forced into the baby’s lungs at high pressure. This can lead to a condition called persistent pulmonary hypertension of the newborn, where the baby struggles to get enough oxygen after birth. Case reports have documented this happening not only with oral NSAIDs but even with topical versions applied to the skin. ACOG is direct on this point: taking ibuprofen during the third trimester “may lead to birth defects.”
When Ibuprofen Might Still Be Used
There is a narrow window where some providers will consider ibuprofen. ACOG notes that for migraines that don’t respond to acetaminophen, ibuprofen may be recommended during the second trimester only, and for no more than 48 hours at a time. This is a specific, supervised exception rather than a green light for casual use. Any decision to take ibuprofen during pregnancy should involve your OB-GYN weighing the severity of your symptoms against the potential risks.
If You Took Ibuprofen Before Knowing You Were Pregnant
A single dose or a few days of ibuprofen before you realized you were pregnant is not the same as sustained use during a vulnerable period. The kidney and amniotic fluid problems the FDA flagged typically develop after days to weeks of treatment, and the ductus arteriosus risk applies mainly to later pregnancy. If you took ibuprofen very early on, before a positive test, the exposure is unlikely to have caused the specific complications described above. That said, mentioning it at your next prenatal visit lets your provider note it in your chart and address any concerns.
What to Take Instead
Acetaminophen (Tylenol) is the recommended first-line option for pain and fever throughout pregnancy. ACOG reaffirms it as the safest analgesic and antipyretic available to pregnant people. The guidance is to use the lowest effective dose for the shortest time you need it. For many common pregnancy complaints like headaches, back pain, and low-grade fevers, acetaminophen is effective enough on its own.
If acetaminophen isn’t managing your pain, that’s a conversation to have with your provider rather than a reason to reach for ibuprofen. There are other approaches, from physical therapy to certain prescription options, that can be tailored to your trimester and situation. The key point is that ibuprofen’s mechanism of action, blocking prostaglandins, interferes with processes the baby actively depends on for normal development, which is why it carries risks that acetaminophen does not.