July 9, 2025

expert reaction to cohort study looking at the use of antibiotics to treat UTIs in the first trimester and risk of birth defects

A cohort study published in JAMA Network Open looks at antibiotic use for UTIs during pregnancy (first trimester) and the risk of birth defects. 

Dr Caroline Ovadia, Clinical Senior Lecturer & Honorary Consultant Obstetrician, University of Edinburgh, said:

“Antibiotic usage is common in pregnancy, and untreated urinary tract infections are thought to be associated with increased risks of pregnancy complications, such as preterm birth. Previous smaller studies have variably suggested that the antibiotic trimethoprim used in the first trimester of pregnancy may be associated with increased risk of fetal development concerns, which may occur by its mechanism of action – trimethoprim can block the action of folic acid, which we know is important in early fetal development. This study reports results from a much larger group of patients, and shows that, for those given trimethoprim plus sulfamethoxazole as a combined antibiotic, the rate of congenital anomaly is very slightly higher – with approximately 1 out of every 145 more patients having a baby with a congenital anomaly than happens with those treated for a urinary tract infection with the penicillin group of antibiotics. This supports current practice recommendations to select alternative antibiotics in the first trimester of pregnancy (while organ development is happening for the fetus), and again the general principles of prescribing in pregnancy: to use the appropriate medication at the lowest effective dose for the shortest effective time. Reassuringly for patients, the antibiotic nitrofurantion was not found to be associated with higher risks of fetal anomalies when used in the first trimester for urinary tract infection treatment, which had been previously suggested in some evidence; similarly the absolute risk of congenital anomalies with antibiotic treatment for urinary tract infection in pregnancy remains low, supporting the benefit of appropriate clinician-led treatment of urinary tract infection in pregnancy.”

‘First-Trimester Antibiotic Use for Urinary Tract Infection and Risk of Congenital Malformations’ by Osmundson et al. was published in JAMA Network Open at 16:00 UK time on Wednesday 9^th July. 

DOI: 10.1001/jamanetworkopen.2025.19544

Declared interests

Dr Carolina Ovadia “I have previously consulted for Mirum Pharmaceuticals and participated in research supported by Mirum Pharmaceutical funding, and been supported to attend scientific meetings by Dr Falk Pharma.”