The Need for Antibiotics During Pregnancy
During pregnancy, physiological changes can make a person more susceptible to infections [1.3.3]. Bacterial infections are common, with urinary tract infections (UTIs), respiratory infections, and group B streptococcus being frequent concerns [1.2.2]. Antibiotics account for a significant portion of prescriptions during pregnancy, with some studies indicating they make up nearly 80% of all prescribed medications [1.2.1]. Untreated infections can pose serious risks, including preterm labor, low birth weight, and other complications for both the mother and the fetus [1.3.6]. Therefore, the careful selection of an antibiotic is a critical decision that balances the benefit of treating the infection against the potential risks to the developing baby.
Understanding Medication Safety: FDA Categories and the PLLR
For decades, the U.S. Food and Drug Administration (FDA) used a letter-based system (A, B, C, D, X) to categorize the potential risk of medications during pregnancy [1.5.1].
- Category A: Controlled studies in women show no risk [1.5.1].
- Category B: Animal studies show no risk, but there are no adequate studies in pregnant women. Many commonly used antibiotics fall into this category [1.5.2, 1.5.3].
- Category C: Animal studies have shown an adverse effect, but potential benefits may warrant use [1.5.2].
- Category D: There is evidence of human fetal risk, but benefits may outweigh risks in certain situations [1.5.2].
- Category X: The risks clearly outweigh any potential benefits [1.5.2].
In 2015, the FDA began phasing out these letter categories in favor of the Pregnancy and Lactation Labeling Rule (PLLR) [1.2.1, 1.5.6]. The PLLR provides a more detailed, narrative summary of risks in three sections: "Pregnancy," "Lactation," and "Females and Males of Reproductive Potential" [1.2.1, 1.4.6]. This newer format is designed to give healthcare providers a more nuanced understanding to better counsel their patients, though many resources still refer to the older letter categories [1.5.6].
Antibiotics Generally Considered Safe
When an antibiotic is necessary, healthcare providers often turn to drugs with a long history of safe use during pregnancy. These medications have been extensively studied and are not associated with an increased risk of birth defects or other fetal harm [1.3.2, 1.3.4, 1.3.7].
Commonly Prescribed Safe Antibiotics:
- Penicillins: This class, including amoxicillin, ampicillin, and penicillin VK, is one of the most commonly prescribed during pregnancy and is considered safe for use in all trimesters [1.3.2, 1.3.5].
- Cephalosporins: Drugs like cephalexin (Keflex) and cefaclor are also widely used and regarded as safe [1.3.2, 1.3.5]. One exception is ceftriaxone, which should be used with caution near the time of delivery due to a risk of kernicterus (a form of brain damage from high bilirubin levels) in the newborn [1.4.3, 1.3.5].
- Clindamycin: This antibiotic is generally considered safe for use throughout pregnancy [1.3.2, 1.3.7].
- Fosfomycin: Often used as a single-dose treatment for UTIs, fosfomycin is considered safe and effective, particularly in the first trimester [1.4.3, 1.7.1].
Antibiotics Used with Caution
Some antibiotics may be safe during certain stages of pregnancy but carry risks in others. Their use requires a careful risk-benefit analysis by a healthcare provider.
- Nitrofurantoin (Macrobid): This is a common treatment for UTIs. While generally considered safe, it is often avoided in the first trimester due to a potential, though debated, link to birth defects [1.4.2, 1.8.3, 1.8.5]. It is also avoided at term (near delivery) because of a small risk of causing red blood cell problems (hemolytic anemia) in the newborn [1.7.2, 1.8.2].
- Metronidazole (Flagyl): Used for certain vaginal infections, systemic use of metronidazole is often avoided in the first trimester if possible [1.4.3]. It is generally considered safe to use with caution in the second and third trimesters [1.4.3].
- Sulfamethoxazole/Trimethoprim (Bactrim): This combination is typically avoided during the first trimester because it interferes with folic acid, which is crucial for development, and has been associated with neural tube defects [1.4.5, 1.6.3]. It is also avoided in the third trimester due to the risk of kernicterus in the newborn [1.4.4, 1.8.5].
Antibiotics to Avoid During Pregnancy
Certain classes of antibiotics are known to pose significant risks to the developing fetus and are generally avoided unless no safer alternative exists for a life-threatening infection.
- Tetracyclines: This class, which includes doxycycline and minocycline, is contraindicated. These drugs can interfere with the development of a baby's bones and cause permanent discoloration (yellow or brown) of their teeth [1.4.2, 1.6.2].
- Fluoroquinolones: This class includes ciprofloxacin (Cipro) and levofloxacin. They have been traditionally avoided due to concerns from animal studies about potential damage to fetal cartilage, bones, kidneys, and the central nervous system [1.4.3, 1.4.5, 1.6.3].
- Aminoglycosides: This class, particularly streptomycin, has been linked to ototoxicity (hearing damage) in the fetus and is generally avoided [1.4.1, 1.4.3]. Other aminoglycosides like gentamicin may be used in short courses for severe infections if the benefits outweigh the risks [1.2.1].
Comparison of Common Antibiotics for Use in Pregnancy
| Antibiotic Class | Examples | General Safety Assessment | Key Considerations |
|---|---|---|---|
| Penicillins | Amoxicillin, Ampicillin | Generally Safe | Widely used with a strong safety record throughout pregnancy [1.3.2, 1.3.5]. |
| Cephalosporins | Cephalexin, Cefaclor | Generally Safe | Another first-choice option. Ceftriaxone should be used with caution at term [1.4.3, 1.3.5]. |
| Tetracyclines | Doxycycline, Minocycline | Avoid | Can cause permanent tooth discoloration and affect bone growth in the fetus [1.4.5, 1.6.2]. |
| Fluoroquinolones | Ciprofloxacin, Levofloxacin | Avoid | Associated with potential cartilage, bone, and organ damage in animal studies [1.4.3, 1.4.5]. |
| Macrolides | Azithromycin, Erythromycin | Use with Caution | Data is conflicting. Azithromycin is generally considered safe, but others have been linked to potential risks [1.4.3, 1.4.5]. |
| Nitrofurantoin | Macrobid | Use with Caution | Avoid in the 1st trimester and at term (near delivery) if possible [1.4.3, 1.8.5]. |
| Sulfonamides | Bactrim | Use with Caution | Avoid in 1st and 3rd trimesters due to risks of birth defects and jaundice [1.4.5, 1.8.5]. |
Conclusion: The Golden Rule is Consultation
Navigating the need for medication during pregnancy can be stressful, but treating bacterial infections is crucial for a healthy outcome. While many antibiotics like penicillins and cephalosporins have a proven safety record, others pose significant risks [1.3.6]. The decision should never be made alone. Always consult with a healthcare provider who can assess the specific infection, consider the stage of pregnancy, and prescribe the safest, most effective antibiotic. Never take leftover antibiotics or medication prescribed for someone else, as this can be dangerous for both you and your developing baby.
Authoritative Link: ACOG - Urinary Tract Infections in Pregnant Individuals
