INTRODUCTION: An increased risk of diagnosed chorioamnionitis in women vaccinated with Tdap during pregnancy was previously detected at two Vaccine Safety Datalink (VSD) sites. The clinical significance of this finding related to infant outcomes remains uncertain. METHODS: Retrospective cohort study of singleton live births born to women who were continuously insured from 6 months prior to their last menstrual period through 6 weeks postpartum, with >/=1 outpatient visit during pregnancy from January 1, 2010 to November 15, 2013 at seven integrated United States health care systems part of the VSD. We re-evaluated the association between maternal Tdap and chorioamnionitis and evaluated whether specific infant morbidities differ among infants born to mothers who did and did not receive Tdap during pregnancy. We focused on 2 Tdap exposure windows: the recommended 27-36 weeks gestation or anytime during pregnancy. We identified inpatient diagnostic codes for transient tachypnea of the newborn (TTN), neonatal sepsis, neonatal pneumonia, respiratory distress syndrome (RDS), and newborn convulsions associated with an infant's first hospitalization. A generalized linear model with Poisson distribution and log-link was used to estimate propensity score adjusted rate ratios (ARR) with 95% confidence intervals (CI). RESULTS: The analyses included 197,564 pregnancies. Chorioamnionitis was recorded in 6.4% of women who received Tdap vaccination any time during pregnancy and 5.2% of women who did not (ARR [95% CI]: 1.23 [1.17, 1.28]). Compared with unvaccinated women, there were no significant increased risks (ARR [95% CI]) for TTN (1.04 [0.98, 1.11]), neonatal sepsis (1.06 [0.91, 1.23]), neonatal pneumonia (0.94 [0.72, 1.22]), RDS (0.91 [0.66, 1.26]), or newborn convulsions (1.16 [0.87, 1.53]) in infants born to Tdap-vaccinated women. CONCLUSIONS AND RELEVANCE: Despite an observed association between maternal Tdap vaccination and maternal chorioamnionitis, we did not find increased risk for clinically significant infant outcomes associated with maternal chorioamnionitis.