The Association of COVID-19 Infection in Pregnancy With Preterm Birth: A Retrospective Cohort Study in California

Background: Our understanding of the association of coronavirus disease 19 (COVID-19) and preterm or early term birth among racially and ethnically diverse populations and those with chronic medical conditions is limited. Methods: We examined the relationship between COVID-19 and preterm (PTB) birth among live births documented by California Vital Statistics birth certificates between July 2020 and January 2021 (n=240,147). We used best obstetric estimate of gestational age to classify births as very preterm (VPTB, <32 weeks), PTB (< 37 weeks), early term (37 and 38 weeks), and term (39-44 weeks), as each confer independent risks to infant health and development. Separately, we calculated the joint effects of COVID-19 diagnosis, hypertension, diabetes, and obesity on preterm and early term birth. Findings: COVID-19 diagnoses on birth certificates increased for all racial/ethnic groups between July 2020 and January 2021, and was highest for American Indian/Alaska Native (12.9%), Native Hawaiian/Pacific Islander (11.4%), and Latinx (10.3%) birthing people. COVID-19 diagnosis was associated with an increased risk of VPTB (aRR 1.6, 95% CI [1.4, 1.9]), PTB (aRR 1.4, 95% CI [1.3, 1.4]), and early term birth (aRR 1.1, 95% CI [1.1, 1.2]). There was no effect modification of the overall association by race/ethnicity or insurance status. COVID-19 diagnosis was associated with elevated risk of PTB in people with comorbidities. Interpretation: In a large population-based study, COVID-19 diagnosis increased the risk of VPTB, PTB, and early term birth, particularly among those with medical comorbidities. Prevention measures, including vaccination, should be prioritized for birthing persons. Funding Information: UCSF-Kaiser Department of Research Building Interdisciplinary Research Careers in Women’s Health Program (BIRCWH) National Institute of Child Health and Human Development (NICHD) and the Office of Research on Women’s Health (ORWH) [K12 HD052163] and the California Preterm Birth Initiative, funded by Marc and Lynn Benioff. Declaration of Interests: The authors have no conflicts of interest to disclose. Ethics Approval Statement: The Committee for the Protection of Human Subjects (CPHS) within the Health and Human Services Agency of the State of California approved study protocols.