First-Trimester Trimethoprim Linked to Increased Birth Defects in Large US Study

Recent large-scale studies have highlighted significant risks associated with the use of the antibiotic trimethoprim-sulfamethoxazole (TMP-SMX) during the first trimester of pregnancy for treating urinary tract infections (UTIs). Research involving over 70,000 pregnancies found that TMP-SMX is linked to an increased risk of congenital malformations, including severe cardiac defects and cleft lip and palate, compared to beta-lactam antibiotics. Although UTIs are common and pose serious risks if untreated, the choice of antibiotic is critical, as trimethoprim may interfere with folic acid metabolism, essential for fetal development. Conversely, nitrofurantoin, another commonly prescribed antibiotic for UTIs, did not show an elevated risk of birth defects, supporting its relative safety in early pregnancy. Experts emphasize the importance of selecting appropriate antibiotics at the lowest effective dose and shortest duration, especially during organogenesis, to minimize fetal risks. These findings align with current recommendations from the American College of Obstetricians and Gynecologists to avoid TMP-SMX and nitrofurantoin in the first trimester when possible, despite their frequent use.