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

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.

This study aimed to determine whether a similar association and protective effect of COVID-19 vaccination on preterm birth would be found in our multistate, US cohort.

A cohort study was conducted using the Vizient Clinical Database, which included data from 192 hospitals in 38 states. Pregnant 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.

Matching with replacement was performed for 5749 treated participants. After propensity score matching, there was no difference in maternal demographics of age, race, insurance status, parity, or comorbid conditions. 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.

Vaccination against COVID-19 may be protective against preterm birth.