The five antibiotic safety categories are A, B, C, D and X. These categories tell the doctor which antibiotics are safe to prescribe during pregnancy and which are not.

Category A includes antibiotics that are known to cause no harm to the fetus. Mycostatin is currently the only antibiotic listed as Category A.

Category B, the most common category, includes antibiotics that are not known to cause birth defects or any pregnancy complications. The antibiotics listed as Category B include Penicillin, Amoxicillin, Ampicillin, Cloxacillin, Flucloxacillin, Cephalexin, Cefradine, Cefuroxime, Cefixime, Cefpodoxime, Cefotaxime, Ceftriaxone, Azithromycin, Erythromycin, Clotrimazole, Metronidazoles and Naproxen.

Category C includes antibiotics that have not been tested on pregnant women enough to provide a definitive result. These antibiotics may have shown negative effects on the fetus in animal studies. Category C antibiotics include Bactrim (also categorized occasionally as category D), Trimethoprim, Biaxin, Cipro, Diflucan, Monistat, Terazol,
Isoniazid, Rifampin, Vermox and Tetanus booster. Hepatitis A, Hepatitis B, Flu, Meningococcus, Pneumonia, Polio and MMR vaccines should also be avoided during pregnancy.

Category D includes antibiotics that are known to cause birth defects or pregnancy complications. The Category D antibiotics include Tetracycline, Doxycycline, Oxytetracycline and Naproxen in the third trimester.

Category X includes antibiotics that have shown fetal risk and / or abnormalities in real life situations in either humans or animals. Category X antibiotics include Isotretinoin and Thalidomide.

With the list of antibiotics constantly growing, this list is not all inclusive. It can take some time for a medication to be listed in the appropriate category as new antibiotics are not often prescribed to patients who are pregnant before they are listed.