Safety facts at a glance
- Decades of use, reassuring data. MotherToBaby, the teratology information service, says most studies of first-trimester use have not found a higher chance of birth defects, and any cleft risk is expected to be low.
- Former FDA category B. Many current amoxicillin labels still print “Pregnancy Category B”: animal studies showed no harm to the fetus, but there are no controlled trials in pregnant women.
- CDC lists it for pregnancy-specific uses. CDC names amoxicillin as an alternative chlamydia treatment in pregnancy and as a first choice (with cefuroxime) for Lyme disease, where doxycycline is generally avoided.
- Augmentin is a separate question. In women whose waters broke early, amoxicillin-clavulanate was linked to a higher rate of a serious newborn bowel condition (NEC) in the large ORACLE I trial.
- Breastfeeding is generally fine. NIH’s LactMed database calls amoxicillin acceptable for nursing mothers; milk levels are low, and the main infant effects reported are loose stools, thrush, or rash.
If you have just been handed a prescription and a positive pregnancy test in the same month, it is natural to pause before taking anything. The good news is that amoxicillin during pregnancy is one of the most studied antibiotic exposures in obstetrics. It is a penicillin-family drug that obstetricians, midwives, dentists, and family doctors reach for often, because both the drug and the infections it treats are well understood.
“Well studied” is not the same as “zero questions,” though. Some research has raised small signals worth knowing about, the combination drug Augmentin carries its own caveat late in pregnancy, and your changing body can affect how fast the drug leaves your system. This guide walks through what the FDA label and the research say, what changes from one trimester to the next, which infections it treats, and what to ask at your next prenatal visit.
What the label and the research say
The FDA label: category B, and why that letter is fading out
For decades, the FDA sorted drugs into pregnancy letter categories A, B, C, D, and X. Amoxicillin sat in category B. If you read a current generic amoxicillin label on DailyMed, the National Library of Medicine’s drug label database, you will still see that wording. The label states that reproduction studies in mice and rats found no evidence of harm to the fetus, that there are no adequate and well-controlled studies in pregnant women, and that the drug should be used in pregnancy only if clearly needed.
That phrase “only if clearly needed” is standard wording. It reflects the fact that randomized trials are rarely run in pregnant women, not a known danger, and it is a reminder that nobody should take amoxicillin during pregnancy “just in case.”
In 2015 the FDA’s Pregnancy and Lactation Labeling Rule (PLLR) began replacing the letters with a written risk summary, clinical considerations, and data. Older labels switch over gradually, which is why many plain amoxicillin labels still say “Category B” while some amoxicillin-clavulanate labels already use the narrative PLLR style.
The label also has a short labor and delivery section. It notes that oral ampicillin, a close cousin, is poorly absorbed during labor, and that the effects of amoxicillin given during labor on the baby, the length of labor, or the need for interventions are not known. We return to that in the trimester section.
What large studies and expert services report
The most practical summary for patients comes from MotherToBaby, a service run by the Organization of Teratology Information Specialists. Its fact sheet on amoxicillin and clavulanic acid, hosted on NCBI Bookshelf, reviews both the combination drug and amoxicillin alone. Key points from the current version:
- Every pregnancy starts with a background risk of birth defects of about 3 to 5 percent, regardless of medicines.
- Most studies have not found that first-trimester use raises that baseline risk.
- Amoxicillin is not expected to raise the chance of preterm delivery or low birth weight.
- A study that followed hundreds of children to age 11 found no link between exposure before birth and learning or behavior problems.
The track record for amoxicillin during pregnancy is so steady that researchers now use the drug as the “safe yardstick” when they test other antibiotics. A 2025 French nationwide study in PLOS Medicine compared first-trimester macrolide use with first-trimester amoxicillin use in more than 590,000 amoxicillin-exposed pregnancies. Danish registry researchers writing in The BMJ in 2021 took a similar approach, using penicillin as the comparison group when they examined macrolides. Choosing a drug as the benchmark does not prove it is risk-free, but it shows how much confidence the field places in the penicillin family.
Studies with signals, and how experts read them
Two signals come up when you dig into the literature on amoxicillin during pregnancy.
Cleft lip and palate. A few studies of amoxicillin alone, including a 2012 U.S. case-control analysis, found a higher chance of cleft lip or palate after first-trimester use. Other studies did not. MotherToBaby’s overall reading is that the chance of a cleft is expected to be low. Case-control studies rely on mothers recalling medicines after a baby is born, and they test many drug and defect pairings at once, so occasional chance findings are expected. A signal that does not repeat across large registries is treated as a reason to keep watching, not as proof of harm.
Miscarriage. Some studies have tied antibiotic use in early pregnancy to miscarriage. The big challenge here is “confounding by indication”: infections themselves, especially with fever, can contribute to pregnancy loss. A widely discussed 2017 study in the Canadian Medical Association Journal that tied antibiotic use to miscarriage used penicillin as one of its comparison drugs in a secondary analysis. MotherToBaby notes that a study of amoxicillin did not find a higher chance of miscarriage.
The trade-off that matters: an untreated bacterial infection in pregnancy is not a neutral choice. A kidney infection, untreated strep, or Lyme disease can carry real risks for you and your baby. When an antibiotic is genuinely needed, a well-studied one like amoxicillin is usually the reassuring option, not the risky one.
Amoxicillin during pregnancy, trimester by trimester
Pregnancy is not one fixed state. What researchers watch for with amoxicillin during pregnancy, and why it gets prescribed, shifts as the weeks go by.
First trimester (weeks 1 to 13)
This is when the baby’s organs form, so it is the window most birth defect research focuses on. The cleft signal described above applies to this period. Even so, the bulk of the evidence on amoxicillin in the first trimester is reassuring, and many people take it before they even know they are pregnant. If that happened to you, a single course of a penicillin antibiotic is not usually considered a reason for alarm, but do tell your prenatal provider so it goes into your record.
Common first-trimester reasons for a prescription:
- Bacteria found in urine at the first prenatal visit. Many practices check a urine culture early in pregnancy, even if you feel fine.
- Strep throat, sinus, or ear infections, which are no less common in early pregnancy.
- Chlamydia found on routine prenatal screening, when the preferred single-dose drug is not an option.
Morning sickness peaks now too. If you vomit soon after a dose, call your pharmacist rather than guessing whether to repeat it.
Second trimester (weeks 14 to 27)
Organ formation is largely finished, and the concern shifts from birth defects toward growth and preterm birth. MotherToBaby says amoxicillin is not expected to increase preterm delivery or low birth weight. This is also the stretch when many people schedule dental work they have been putting off, so tooth abscesses and post-procedure infections come up more often.
One reason amoxicillin becomes even more attractive mid-pregnancy: some alternatives drop off the table. CDC’s STI guidelines state that doxycycline is contraindicated in the second and third trimesters because of the risk of tooth discoloration in the baby. That leaves penicillins and a few other classes doing more of the work.
Third trimester (weeks 28 to 40)
Late pregnancy brings its own reasons for antibiotics. Urinary infections can climb toward the kidneys more easily as the growing uterus presses on the urinary tract. If your waters break early, before 37 weeks, an antibiotic course may be started in the hospital to buy time and lower infection risk. That is where the distinction between amoxicillin and Augmentin becomes important, which we cover below.
This is also when you will be screened for group B streptococcus (GBS). GBS is not treated with a course of pills during pregnancy; instead, if you test positive, you get IV antibiotics during labor.
Labor and delivery
During labor, antibiotics are usually given through an IV rather than by mouth. The amoxicillin label notes that oral ampicillin is poorly absorbed during labor, which is one reason hospitals use the IV route. For GBS, CDC’s group B strep prevention guidance says beta-lactam drugs such as penicillin or ampicillin are the most common choices.
A 2008 Dutch study in the British Journal of Clinical Pharmacology measured IV amoxicillin levels in 34 women before and during labor. Labor and swelling shifted how the drug spread through the body, but the authors judged the changes not clinically relevant and saw no need to alter standard dosing for healthy women in labor.
Infections amoxicillin treats during pregnancy
Here is how amoxicillin during pregnancy fits into the care of infections that commonly come up in pregnancy, based on the guideline or source noted. Durations shown are those named in the cited guideline, for reference only.
| Infection | Where amoxicillin fits | Pregnancy-specific notes |
|---|---|---|
| Asymptomatic bacteriuria or bladder infection (UTI) | One of several oral options once the urine culture shows the germ is sensitive | ACOG’s 2023 clinical consensus advises against starting amoxicillin before culture results because many E. coli strains are resistant; untreated bacteriuria in pregnancy can progress to kidney infection |
| Strep throat | First-line (penicillin or amoxicillin), typically 10 days per IDSA | Same approach as outside pregnancy; allergy alternatives exist |
| Sinus and ear infections | Common choice when a bacterial cause is likely | Many sinus infections are viral and do not need antibiotics at all |
| Dental infections | Common choice alongside dental treatment | Draining or treating the tooth is the main fix; antibiotics support it |
| Early Lyme disease (erythema migrans rash) | CDC lists amoxicillin 500 mg three times daily for 14 days for adults | CDC’s pregnancy fact sheet names oral amoxicillin or cefuroxime; doxycycline is generally not used in pregnancy |
| Chlamydia | CDC 2021 alternative: amoxicillin 500 mg three times daily for 7 days | Azithromycin 1 g once is preferred; a test of cure about 4 weeks after treatment is recommended in pregnancy |
| H. pylori (stomach ulcer bacteria) | Part of multi-drug regimens outside pregnancy | Treatment is often postponed until after delivery unless symptoms are severe, because regimens include other drugs |
| Preterm prelabor rupture of membranes (PPROM) | Hospital “latency” regimen: IV ampicillin plus erythromycin, then oral amoxicillin plus erythromycin (ACOG 2020) | Azithromycin is often substituted for erythromycin; amoxicillin-clavulanate is avoided because of the NEC signal |
Urinary infections. Pregnancy is one of the few times doctors treat bacteria in the urine even when you have no symptoms, because of the risk of kidney infection. Amoxicillin can work well when lab testing confirms the bacteria are sensitive, but it is rarely a blind first pick for that reason. Our guide on whether amoxicillin can treat a UTI explains the resistance issue in more depth.
Lyme disease. CDC’s Lyme disease fact sheet for pregnant women states that, with appropriate antibiotic treatment, there is no increased risk of adverse birth outcomes. It names oral amoxicillin or cefuroxime as treatment and says drugs like doxycycline are generally not used in pregnancy. If you find a tick or a spreading rash, call your provider promptly instead of waiting for your next appointment.
Chlamydia. The CDC 2021 STI treatment guidelines for chlamydia list azithromycin as the recommended pregnancy regimen and amoxicillin as the alternative. Amoxicillin sits second partly because of concern that the chlamydia organism can persist after penicillin-class exposure, which is one reason a test of cure is so important.
Dental infections. Pregnancy gum changes make dental problems more likely, and delaying treatment of an abscess can make things worse. If your dentist prescribes an antibiotic, read our guide to amoxicillin for a tooth infection for what to expect, and make sure the dental office knows you are pregnant.
Amoxicillin vs Augmentin in pregnancy
Augmentin is amoxicillin plus clavulanic acid (clavulanate), an ingredient that blocks an enzyme some bacteria use to destroy amoxicillin. That broadens the range of germs it covers. For most everyday infections in pregnancy, the safety picture for the two is similar. The notable exception involves one specific situation: preterm prelabor rupture of membranes.
What the ORACLE I trial found
ORACLE I, published in The Lancet in 2001, enrolled 4,826 women whose waters had broken before labor and before term. They were randomly assigned to erythromycin, amoxicillin-clavulanate, both, or placebo. Erythromycin showed several benefits for newborns. Amoxicillin-clavulanate, alone or with erythromycin, was linked to a significantly higher rate of necrotizing enterocolitis (NEC), a serious inflammation of the newborn’s intestines that mostly affects premature babies.
Amoxicillin-clavulanate labels that use the newer PLLR format now describe this finding: in that trial, proven NEC occurred in 1.9 percent of newborns in the amoxicillin-clavulanate-only group compared with 0.5 percent in the placebo group. MotherToBaby describes the absolute risk as likely low, while noting that other antibiotics may be preferred after early rupture of membranes.
What this does and does not mean for you
- It does mean hospitals generally avoid amoxicillin-clavulanate for early rupture of membranes, and use plain ampicillin and amoxicillin with a macrolide instead.
- It does not mean that a course of Augmentin for a sinus infection at 10 weeks caused harm. The NEC signal was found in a very specific group of women at risk of delivering a premature baby.
- It is fair to ask, if you are prescribed Augmentin late in pregnancy, whether plain amoxicillin would work just as well. Sometimes the infection truly needs the broader coverage.
Augmentin also tends to cause more stomach upset and diarrhea than plain amoxicillin. For a full side-by-side on coverage, cost, and side effects, see our amoxicillin vs Augmentin comparison.
Body changes that affect dosing
Amoxicillin leaves the body mainly through the kidneys, and pregnancy speeds the kidneys up a lot, which is why dosing amoxicillin during pregnancy has drawn research interest. A 2019 systematic review in Ultrasound in Obstetrics & Gynecology found that the glomerular filtration rate (a measure of how fast the kidneys filter blood) rises by up to 40 to 50 percent as early as the first trimester. Your blood volume also expands, giving the drug more space to spread out.
Put together, that means a given dose may produce lower levels and clear faster in pregnancy. A 2007 study by Andrew and colleagues in Clinical Pharmacology & Therapeutics confirmed increased amoxicillin clearance in pregnant women. The FDA’s commentary on amoxicillin dosing for anthrax exposure used that work to model how pregnancy changes drug levels, and concluded that some second-trimester women would dip below target levels between doses on standard schedules.
What does that mean in practice?
- Timing matters. Spacing doses evenly across the day helps keep levels steady. If your prescription says every 8 hours, try to stick close to that rather than bunching doses around meals.
- Your prescriber may pick a regimen with this in mind. Label regimens for adults include 500 mg every 12 hours or 250 mg every 8 hours for mild to moderate ear, nose, throat, skin, and urinary infections, and 875 mg every 12 hours or 500 mg every 8 hours for more severe ones. Guideline regimens for specific infections, like the ones in the table above, can differ.
- Do not adjust on your own. Never double up or add extra doses because you read that clearance is faster. Follow your own prescription, and ask your pharmacist if you are unsure about timing.
For a fuller explanation of how label doses are built and why they vary by infection, see our amoxicillin dosage guide.
Side effects that matter more when pregnant
The FDA label lists diarrhea, rash, vomiting, and nausea as the most common side effects of amoxicillin, and these are also the ones people notice most when taking amoxicillin during pregnancy. None of these are unique to pregnancy, but a few of them land differently when you are expecting.
Vaginal yeast infections
Pregnancy hormones already make yeast infections more common, and antibiotics can tip the balance further by clearing out protective bacteria. CDC’s guidelines list frequent antibiotic use as one possible trigger of recurrent yeast infections.
The treatment rules change in pregnancy. The CDC guideline on vulvovaginal candidiasis recommends only topical azole creams or suppositories, used for 7 days, during pregnancy, and advises against oral fluconazole. So if itching or discharge shows up during or after your course, check with your provider before grabbing a pill you may have used in the past.
Diarrhea and dehydration
Mild loose stools are common and usually settle after the course ends. In pregnancy, though, fluid loss adds up faster, especially if you are also dealing with morning sickness. Sip fluids steadily, and call your provider if you cannot keep liquids down, feel dizzy, or notice you are urinating much less.
Rarely, antibiotics allow an overgrowth of Clostridioides difficile, which causes severe, watery, sometimes bloody diarrhea. The label warns this can start up to two months after the last dose. Do not take anti-diarrhea medicine on your own if diarrhea is severe or bloody; call your provider. Our article on amoxicillin and diarrhea covers the warning signs and what tends to help.
Allergic reactions
The label warns that serious and occasionally fatal allergic reactions (anaphylaxis) have been reported with penicillins. Anaphylaxis is dangerous for anyone, and in pregnancy a sharp drop in blood pressure can also reduce blood flow to the baby. Call 911 for hives with swelling of the lips, tongue, or throat, wheezing, trouble breathing, or fainting.
On the flip side, many people carry a “penicillin allergy” label from a childhood rash that was never a true allergy, which can push doctors toward less-studied antibiotics. If yours is old and vague, ask whether testing to clarify it makes sense. Our guide to amoxicillin allergy explains the difference between a true allergy and a harmless rash.
Amoxicillin while breastfeeding
Once your baby arrives, the question shifts from the placenta to breast milk. Here the evidence is about as reassuring as it gets for an antibiotic. The NIH’s LactMed entry on amoxicillin, last revised in June 2026, says milk levels are low, are not expected to harm breastfed infants, and that amoxicillin is acceptable for nursing mothers.
Just how low? LactMed estimates that if a mother takes 500 mg three times a day, an exclusively breastfed baby would get at most about 0.1 mg/kg per day. That is roughly 0.25 to 0.5 percent of a typical infant amoxicillin dose. A newer study of 25 mothers estimated the relative infant dose stayed below 0.4 percent even with high maternal doses, and reported no effect on milk supply.
What to watch for in your baby
Even tiny amounts can affect a baby’s gut bacteria. In LactMed’s summary of the studies, the reported effects were mostly minor and short-lived:
- Loose stools or diarrhea, reported in about 5 to 12 percent of exposed infants across small studies
- Thrush (white patches in the mouth) or diaper rash from yeast
- Skin rash, which is uncommon
The FDA label adds that amoxicillin in milk could, in theory, sensitize an infant to penicillins. Call your baby’s pediatrician if your baby develops a rash, persistent diarrhea, poor feeding, or mouth patches while you are taking an antibiotic. For Augmentin, MotherToBaby notes a study of 67 breastfed infants with no serious side effects; some babies had brief rash, diarrhea, irritability, or constipation.
Questions to bring to your OB or midwife
A short list can make a rushed appointment much more useful. Pick the ones that fit your situation:
- Is this infection definitely bacterial, or could it clear on its own?
- Was a culture or test done, and does it show the bacteria are sensitive to amoxicillin?
- Is plain amoxicillin enough, or do I need Augmentin? If Augmentin, why?
- How exactly should I space my doses, and what should I do if I vomit one?
- Do I need a follow-up test (for example, a repeat urine culture or a chlamydia test of cure) after I finish?
- I have a penicillin allergy on my record. Should it be checked or cleared before my due date?
- What symptoms during the course mean I should call you right away?
- If I get a yeast infection, which treatment is safe for me now?
- I took amoxicillin before I knew I was pregnant. Does anything need to change in my care?
- I plan to breastfeed. Will this or any antibiotic I might need after delivery affect that?
If you are weighing other medicines too, our other pregnancy medication guides cover albendazole in pregnancy and Adderall during pregnancy and breastfeeding.
Safe-use reminders
- Take only amoxicillin prescribed for you, for this infection. Leftover pills from an old prescription, or a partner’s supply, may be the wrong drug, dose, or length of course.
- Finish the course as prescribed unless your provider tells you to stop.
- Tell every prescriber, including your dentist and urgent care, that you are pregnant or breastfeeding.
- Seek urgent care for fever with back pain, signs of an allergic reaction, fluid leaking from the vagina, or severe abdominal pain.
Medical disclaimer: This pregnancy guide draws on published sources available as of October 2026. It is not medical advice and cannot account for your health history, allergies, or the details of your pregnancy. Decisions about starting, changing, or stopping any medicine during pregnancy or breastfeeding should be made with your obstetrician, midwife, or other licensed clinician. If you think you are having an allergic reaction or a pregnancy emergency, call 911 or go to the nearest emergency department.
References
- Amoxicillin prescribing information (Sandoz, rev. 2/2024). DailyMed, NLM.
- FDA. Pregnancy and Lactation Labeling Final Rule.
- MotherToBaby (OTIS). Amoxicillin and Clavulanic Acid fact sheet. NCBI Bookshelf.
- Tran et al. Macrolides vs amoxicillin and major congenital malformations: French nationwide cohort. PLOS Med, 2025.
- Andersson NW, et al. Macrolides in pregnancy and major birth defects. BMJ 2021;372:n107.
- Kenyon SL, et al. ORACLE I randomised trial. Lancet 2001;357:979-988.
- ACOG Practice Bulletin No. 217: Prelabor Rupture of Membranes, 2020.
- ACOG Clinical Consensus No. 4: Urinary Tract Infections in Pregnant Individuals, 2023.
- CDC. STI Treatment Guidelines, 2021: Chlamydial Infections; Vulvovaginal Candidiasis.
- CDC. Clinical Treatment of Erythema Migrans Rash (2026); Pregnancy and Lyme Disease fact sheet; Preventing Group B Strep Disease in Newborns.
- IDSA. Group A streptococcal pharyngitis guideline, 2012 update.
- van Balen VAL, et al. Maternal kidney function during pregnancy. Ultrasound Obstet Gynecol 2019;54:297-307.
- Andrew MA, et al. Clin Pharmacol Ther 2007;81:547-556; FDA commentary on oral amoxicillin dosing for anthrax.
- Muller AE, et al. Br J Clin Pharmacol 2008;66:866-874.
- LactMed. Amoxicillin. NICHD, revised June 2026.
- Minnesota Department of Health. H. pylori FAQ.
