Few studies have evaluated the association between periodontitis and spontaneous abortion (SAB), and all have limitations. We used data from Pregnancy Study Online (PRESTO), a prospective preconception cohort study of 3,444 pregnancy planners (2019-2022). Participants provided self-reported data on periodontitis diagnosis, treatment, and symptoms of severity (i.e., loose teeth) via the enrollment questionnaire. SAB (pregnancy loss <20 weeks' gestation) was assessed via bi-monthly follow-up questionnaires. Participants contributed person-time from the date of positive pregnancy test to the gestational week of SAB, loss-to-follow-up, or 20 weeks' gestation, whichever came first. We fit Cox regression models with gestational weeks as the time scale to estimate adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) and used inverse probability weighting to account for differential loss-to-follow-up. We used probabilistic quantitative bias analysis (QBA) to estimate the magnitude and direction of exposure misclassification bias on results. In weighted multivariable models, we saw no appreciable association between preconception periodontitis diagnosis (HR=0.97, 95% CI 0.76, 1.23) or treatment (HR=1.01, 95% CI 0.879, 1.27) and SAB. A history of loose teeth was positively associated with SAB (HR=1.38, 95% CI 0.88, 2.14). QBA indicated our findings were biased towards the null but with considerable uncertainty in the bias-adjusted results.
