Reduction in preterm birth among COVID-19 -vaccinated pregnant individuals in the United States

BACKGROUND: Most studies investigating preterm birth and COVID-19 vaccination have suggested no difference in preterm birth rates between vaccinated and unvaccinated pregnant individuals; however, 1 recent study suggested a protective effect of COVID-19 vaccination on preterm birth rates in Australia.OBJECTIVE: This study aimed to determine whether a similar associa-tion and protective effect of COVID-19 vaccination on preterm birth would be found in our multistate, US cohort.STUDY DESIGN: A cohort study was conducted using the Vizient Clin-ical Database, which included data from 192 hospitals in 38 states. Preg-nant individuals who delivered between January 2021 and April 2022 were included. Propensity score matching was used to match a "treated" group of pregnant individuals with any COVID-19 vaccination (incomplete or complete vaccination) to a group that had not received any COVID-19 vaccination (the "untreated" group). A complete vaccination series of >= 2 doses of the Moderna or Pfizer vaccines or at least 1 dose of the Johnson & Johnson vaccine was considered. An incomplete series was receipt of 1 dose of the Pfizer or Moderna vaccine. We examined the association between COVID-19 vaccination status and preterm birth at <28, <34, and <37 weeks of gestation. Multivariable logistic regression models were used to adjust for potential confounders, with adjusted odds ratios as the measure of treatment effect.RESULTS: Matching with replacement was performed for 5749 treated participants. After propensity score matching, there was no difference in mater-nal demographics of age, race, insurance status, parity, or comorbid condi-tions. Vaccinated individuals were 26% less likely to deliver at <37 weeks of gestation (adjusted odds ratio, 0.74; 95% confidence interval, 0.73-0.75; P<.001), 37% less likely to deliver at <34 weeks of gestation (adjusted odds ratio, 0.63; 95% confidence interval, 0.61-0.64; P<.001), and 43% less likely to deliver at <28 weeks of gestation (adjusted odds ratio, 0.57; 95% confidence interval, 0.55-0.60; P<0.001) than unvaccinated individuals.CONCLUSION: Vaccination against COVID-19 may be protective against preterm birth.