Urinary tract infections (UTIs) in pregnancy are common—and when left untreated, they can lead to serious maternal and neonatal complications. But choosing the right antibiotic, especially in the first trimester of pregnancy, is critical due to the potential risk of congenital malformations.
So, which antibiotics are safest to use in early pregnancy?
Study Overview: Antibiotics and Birth Defects in Early Pregnancy
A major cohort study published in JAMA Network Open (2025) by researchers at the Washington University School of Medicine explored this exact question. They evaluated the risk of congenital malformations in babies born to individuals who were treated with different oral antibiotics for first-trimester UTIs between 2006 and 2022.
The study analyzed data from 71,604 pregnant individuals, aged 15–49 years, who were treated during the first trimester. The focus was on four commonly used antibiotics:
- Beta-lactams (e.g., penicillins, cephalosporins) – used as the reference group due to established safety
- Nitrofurantoin
- Trimethoprim-sulfamethoxazole (TMP-SMX)
- Fluoroquinolones (e.g., ciprofloxacin, levofloxacin, ofloxacin)
Key Findings: Which Antibiotics Carry the Lowest Risk?
The risk of any congenital malformation (per 1,000 infants) varied by antibiotic:
- Beta-lactams: 19.8
- Nitrofurantoin: 21.2
- Fluoroquinolones: 23.5
- TMP-SMX: 26.9
Risk Ratios (compared to beta-lactams):
- Nitrofurantoin: RR 1.12
- Fluoroquinolones: RR 1.18
- TMP-SMX: RR 1.35
While nitrofurantoin and fluoroquinolones did not show a statistically significant increased risk of birth defects, TMP-SMX was linked to a higher risk, particularly for:
- Severe cardiac malformations: RR 2.09
- Other cardiac defects: RR 1.52
- Cleft lip and palate: RR 3.23
This translated to one additional congenital malformation per 145 pregnant individuals treated with TMP-SMX instead of beta-lactams.
What This Means for UTI Treatment in Pregnancy
Based on the study, the safest antibiotics for UTI treatment during the first trimester appear to be:
- Beta-lactams – first choice due to their strong safety profile
- Nitrofurantoin – relatively safe, but often used later in pregnancy
- Fluoroquinolones – not associated with a higher risk, but typically not first-line
- Avoid TMP-SMX in early pregnancy when possible due to its higher risk of congenital malformations
Why This Matters for Pregnant Individuals
If you’re pregnant and experiencing symptoms of a urinary tract infection, early treatment is essential—but so is choosing the right antibiotic. Always consult your healthcare provider and discuss which antibiotic is safest for you and your baby.
At Pill4me, we understand that pregnancy health decisions can be overwhelming. That’s why we stay on top of the latest research to help you and your doctor make informed choices about safe medication during pregnancy.
Reference:
Osmundson SS, Nickel KB, Shortreed SM, et al. First-trimester antibiotic use for urinary tract infection and risk of congenital malformations. JAMA Network Open. 2025;8(7):e2519544. Accessed July 15, 2025.
What This Means for the Public
This new research is important for anyone who is pregnant or planning to become pregnant. Here’s what you need to know:
- UTIs are common in pregnancy, especially in the first trimester. They need to be treated quickly to avoid complications.
- However, not all antibiotics are equally safe during early pregnancy. Some may slightly increase the risk of birth defects.
- The study shows that beta-lactam antibiotics (like penicillin and cephalosporins) are the safest option when treating UTIs in the first trimester.
- Nitrofurantoin and fluoroquinolones do not appear to significantly increase risk, but they are usually not the first choice unless necessary.
- Trimethoprim-sulfamethoxazole (TMP-SMX) should be avoided during early pregnancy if possible, as it was linked to a higher risk of birth defects, especially heart problems and cleft lip/palate.
Why It Matters:
When a pregnant person is prescribed an antibiotic, the choice of medication can impact the baby’s health. This study helps doctors and patients make safer decisions about which antibiotics to use.
If you’re pregnant and prescribed an antibiotic for a UTI, don’t panic—just make sure to ask your doctor if it’s one of the safer options.
The bottom line: Early treatment is important, but choosing the right antibiotic matters.