Antibiotics are widely used during pregnancy to prevent or treat infections, yet concerns remain regarding their fetal safety. Drawing on data from spontaneous reporting databases and cohort studies, this study aims to explore potential associations between exposure to various antibiotic classes during pregnancy and congenital malformations.

Data were collected from publicly available reports in the U.S. Food and Drug Administration's Adverse Event Reporting System (FAERS), the Canada Vigilance Adverse Reaction (CVAR) database, and a population-based retrospective cohort in Xiamen, China. By applying multiple signal detection methods, we identified potential risk signals linking different antibiotic classes to organ-system-specific congenital malformations. For antibiotics showing positive signals, we further utilized a pregnancy medication cohort in Xiamen and applied causal inference techniques to estimate the adjusted relative risk of congenital malformations associated with first-trimester exposure to these antibiotics. Several sensitivity analyses-including both negative- and positive-control analyses-will also be performed.

Inclusion Criteria:

• For the spontaneous reporting data study, all adverse reactions reported by mothers were included.

For the cohort study, all Xiamen pregnant women registered in the cohort were included

Exclusion Criteria:

• For studies using spontaneous reporting data, all adverse reaction reports unrelated to pregnant or postpartum women-including those occurring during the lactation period-were excluded.

For cohort studies, pregnant women who were lost to follow-up were excluded, and pregnant women who were exposed to factors known to be associated with congenital malformations were excluded.

For the spontaneous reporting studies, the study population was pregnant women who reported an adverse medication event during the study period, where the exposed population was pregnant women who reported an adverse event due to the use of a different type of antibiotic during the study period.

For cohort studies, the study population was women who were pregnant during the study period and the exposed population was pregnant women who used different types of antibiotics during the study period