Antibiotics often are prescribed during pregnancy. And they're always used during C-sections. But only some antibiotics seem OK to take during pregnancy. Others are not.

Safety depends on many factors. These include the type of antibiotic, when in pregnancy you take the antibiotic and for how long, and how much you take.

Here are some antibiotics thought of as safe to take while pregnant:

• Penicillins, including amoxicillin (Amoxil, Larotid) and ampicillin.
• Cephalosporins, including cefaclor and cephalexin.
• Clindamycin (Cleocin, Clinda-Derm, others).
• Metronidazole (Flagyl, Metrogel, others).

Other antibiotics are thought to pose risks during pregnancy. For example, tetracyclines can affect bone growth and cause a baby's teeth to discolor. Tetracyclines aren't suggested for use after the fifth week of pregnancy. Nitrofurantoin (Furadantin) might raise the risk of cleft lip if given in the first trimester. But it's safe to use in the second and third trimesters.

Macrolide antibiotics such as erythromycin, clarithromycin and azithromycin have been linked to heart rhythm conditions and preterm birth in fetuses. But some studies suggest macrolides such as azithromycin may be safe in pregnancy when needed for some sexually transmitted infections, for preterm premature rupture of membranes, and as added therapy for cesarean deliveries after labor has begun. More study is needed.

If an antibiotic is the best way to treat a condition during pregnancy, a healthcare professional prescribes the safest medicine in the safest dose. If you're worried about using an antibiotic during pregnancy, talk to your healthcare professional.