Sometimes there is a need to take antibiotics during pregnancy. A recent study of 182,369 pregnant women found that the use of certain antibiotics during early pregnancy was linked with a higher rate of miscarriage before 20 weeks. These antibiotics included quinolones (Avelox, Cipro, Levaquin, Tequin), tetracyclines, sulfonamides (Septra, Bactrim), metronidazole (Flagyl), and macrolides (such as azithromycin, clarithromycin, but not erythromycin).
Certain antibiotics were not associated with spontaneous abortions. These antibiotics were penicillins, cephalosporins, nitrofurantoin, and erythromycin. The researchers pointed out that nitrofurantoin is a good antibiotic option for urinary tract infections - which is one of the most common infections in pregnancy. From Medscape:
Antibiotics During Pregnancy May Increase Miscarriage Risk
Use of certain antibiotics early in pregnancy is associated with an increased risk for spontaneous abortion, the authors of a new study report. Macrolides (except erythromycin), quinolones, tetracyclines, sulfonamides, and metronidazole all were associated with a greater risk, compared with penicillins, cephalosporins, or no antibiotic exposure at all, Flory T. Muanda, MD, and colleagues write in an article published in the May 1 issue of CMAJ.
To assess the potential effect of antibiotics on miscarriage risk, Dr Muanda, from the Faculty of Pharmacy, Université de Montréal, Quebec, Canada, and colleagues analyzed data from the Quebec Pregnancy Cohort on pregnancies that occurred between January 1998 and December 2009....Women who experienced a clinically detected spontaneous abortion before gestational week 20 were considered cases, with the calendar date of the spontaneous abortion designated the index date. Antibiotic exposure was defined as "having filled at least 1 prescription for any type of antibiotic either between the first day of gestation and the index date, or before pregnancy but with a duration that overlapped the first day of gestation," the authors explain.
Antibiotic exposure occurred in 12,446 (13%) of those pregnancies, including 1428 that ended in spontaneous abortion (16.4% of all pregnancies ending in spontaneous abortion). Among the control patients, 11,018 (12.6% of all controls) were exposed to antibiotics.
In some instances, these findings support data from other studies, the authors point out. The class effect observed of tetracyclines and quinolones "supports current guidelines used in obstetrics that do not recommend use of these drugs in early pregnancy." Their finding that metronidazole was associated with a 70% increase in the risk for spontaneous abortion is similar to that of a study among Medicaid patients showing a 67% increased risk.... No increased risk was associated with nitrofurantoin, erythromycin, penicillins, or cephalosporins.