Receipt of Tdap or Influenza Vaccine During Pregnancy and Odds of Clinical Chorioamnionitis: A Nested Case-Control Study.

Objective: To evaluate the odds of clinical chorioamnionitis following tetanus, diphtheria, and acellular pertussis (Tdap) or influenza vaccine receipt in pregnancy.

Methods: In this nested case-control study, a cohort of live deliveries at two United States military hospitals, 2013-2018, was initially screened for chorioamnionitis using diagnosis codes. A sample of deliveries was selected for chart review and validation. Study cases (clinical chorioamnionitis) were defined by the presence of fever and at least one additional clinical symptom during the delivery hospitalization; controls were defined by the absence of these criteria. Descriptive statistics compared characteristics of validated cases and controls, and multivariable logistic regression models estimated adjusted odds ratios (aORs) and 95% confidence intervals (CIs) with receipt of Tdap or influenza vaccine during pregnancy; observations were weighted by the inverse probability of being sampled for validation.

Results: Among 6931 deliveries, 1868 were sampled for validation and 1650 (n = 305 cases, n = 1345 controls) were included for analysis. At delivery, mean age was 25.0 years for cases and 25.9 years for controls; 88.4% of cases and 63.0% of controls were primipara. Tdap vaccine was recorded in 82.8% of cases and 82.0% of controls (aOR 0.94, 95% CI 0.72, 1.23) and influenza vaccine was recorded in 61.8% of cases and 63.0% of controls (aOR 0.97, 95% CI 0.78, 1.19). Analyses that considered timing and combinations of vaccine receipt yielded similar estimates.

Conclusion: In this population, neither Tdap nor influenza vaccine receipt during pregnancy was associated with increased odds of clinical chorioamnionitis at delivery.