Objective: This study explored maternal knowledge of pertussis and Tdap vaccine and the use of a Tdap Vaccine Information Statement (VIS) to improve that knowledge. Design: Prospective cohort study. Setting: Two outpatient obstetric clinics at a US academic medical centre. Methods: An electronic survey was administered to pregnant women who received care at the clinics. The survey included a test of knowledge of pertussis and Tdap vaccine, a health literacy instrument and demographic questions. A chart review was conducted to determine Tdap vaccination status. The knowledge test was administered before and immediately after participants read the VIS. Differences between pre- and post-knowledge test scores were determined using the Wilcoxon signed-rank test. The effects of two different versions of the VIS on participants' knowledge gained and associated factors were examined using a repeated-measures mixed model with random effects. Results: In total, 279 participants were analysed with an average age of 26.4 ± 5.7 years. The average post-test knowledge score was higher than the pre-test score (6.4 vs 4.2, p < 0.001). Health literacy score (p < 0.001), White race/ethnicity (p = 0.007) and higher education level (p < 0.001) were positively associated with improved knowledge scores. Both VIS versions improved participants' knowledge scores to a similar degree. However, knowledge scores were not a predictor of Tdap vaccination in our population. Conclusion: A Tdap VIS improved maternal knowledge and is an economical and easily accessible educational tool in clinical practice for promoting Tdap vaccine to pregnant women.