Epidemiological studies in humans correlate perinatal dysbiosis with increased long-term asthma severity. However, these studies suffer from high variability of dysbiotic causes (e.g. birth mode, breastfeeding, antibiotic treatment (AbT)). Further, the time window of these factors influencing asthma remains undefined. Given that maternal antibiotic exposure in mice increases the risk of newborn bacterial pneumonia in offspring, we hypothesized that dysbiosis occurring immediately before birth, and shortly after birth, stimulates long-term immunological effects in the offspring leading to an aggravated asthma phenotype. To test this, pregnant and nursing dams underwent AbT from embryonic day 15 until postnatal day 28 (E₁₅-P₂₈). At six weeks of age, experimental allergic asthma (AA) was induced in offspring by four weekly repeated applications of house dust mite extract. 72 h after the last immunization step, airway hyperreactivity (AHR) and pulmonary cell composition were assessed. AbT aggravated AA as characterized by elevated AHR and an increase of cellular infiltrates to the airways site independently at two institutions, excluding a site-specific microbial impact. To further refine the developmental window wherein AbT influences the AA phenotype, we reduced maternal AbT to E₁₅-P₁₄. Surprisingly, E₁₅-P₁₄ AbT-exposed litters did not display altered AA development compared to controls. Combining this data with our previous data demonstrating that AbT from P₁₀-P₂₀ augments AA, indicates that pre- and perinatal AbT is less critical for later-in-life asthma development. This will allow to investigate of the underlying immunological mechanisms during the more decisive later postnatal timeframe in future studies.