What is driving the decreased incidence of preterm birth during the COVID-19 pandemic?

BACKGROUND: Institutions across the world have observed a decrease in preterm birth during the COVID-19 pandemic. The reason for this reduction remains unknown. OBJECTIVE: We sought to explore potential causes of the decrease in preterm birth exploring three hypotheses: 1. Do women who are more likely to be able to work from home incur less physical and/or emotional stress resulting in longer gestation? 2. Does the effect of COVID-19 on preterm birth vary by race? 3. Is the change provider driven? STUDY DESIGN: Using a retrospective cohort of all singleton deliveries at a single tertiary care center, we compared deliveries prior to COVID-19 (1/1/2018-1/31/2020) to those occurring during the pandemic (4/1/2020-10/27/2020). Comparisons were made pre- and post-COVID using Pearson's chi-square or t-tests as appropriate. Preterm birth, defined as delivery at <37 weeks' gestation, was analyzed overall then further classified into spontaneous and indicated. The population was then stratified by: 1. Insurance type and neighborhood disadvantage, 2. Race, and 3. Provider type. Provider type was classified as within an OPC, a clinic that provides prenatal care to those eligible for Medical Assistance, compared with non-OPC. RESULTS: In a population of 17,687 pre-COVID deliveries, and 5,396 post-COVID deliveries, there was a significant decrease in overall preterm birth (11.1 vs. 10.1%; p=0.039). Both spontaneous and indicated preterm deliveries decreased in the full population. When stratified, decreases in spontaneous preterm birth pre- versus post-COVID, were limited to deliveries to women from more advantaged neighborhoods (most advantaged: 4.4 vs. 3.8%; least advantaged: 7.2 vs. 7.4%), white mothers (white: 5.6 vs. 4.7%; black: 6.6 vs. 7.1%), and those receiving care from non-OPC providers (non-OPC providers: 5.5 vs 4.8%; OPC-providers: 6.3 vs 6.7%). CONCLUSIONS: Preterm birth has decreased during the COVID-19 pandemic. Decreases in spontaneous preterm birth were limited to deliveries in white women, living in more advantaged neighborhoods and delivered by non-OPC providers. COVID-19 response regulations may have disproportional benefits to women with more indicators of advantage.