Penicillins and cephalosporins in pregnancy remain the safest options regardless of trimester
Nitrofurantoin and sulfonamides have mixed data:
1st trimester: there are case-control studies that show a link between usage in first trimester and birth defects. Prescribing nitrofurantoin or sulfonamides in first trimester is still considered appropriate when no other suitable alternative is available.
2nd and 3rd trimester: Nitrofurantoin and sulfonamides may continue to be used as first-line agents
Contraindication: Patients with G6PD deficiency