For treating Candida Vaginitis in early pregnancy, ACOG recommends local treatment instead of oral diflucan. This is based on studies that show higher doses (400-800 mg) of oral diflucan has been linked to birth defects. Although a 2013 NEJM cohort study found no association between diflucan and birth defects.
When treating pregnancy women for a UTI in early pregnancy, Nitrofurantoin or Bactrim are both not recommended as a first line agent. A Case-Control study published in 2009 showed an association between treatment with these medications in first trimester and malformations. While there are several limitations to this study, ACOG recommends avoiding these two medications in the first trimester. During the 2nd and 3rd trimester, sulfonamides and nitrofurantoin may be used as first-line therapy. Prescribing these in the first trimester is still considered appropriate when no other alternative is available.
Penicillins, erythromycin, and cephalosporins have not been found to have any associations with birth defects.