Results
There were 1,153 deliveries at Mass General Brigham hospitals during the study time period. Four patients who were not tested for SARS-CoV-2 and six who tested positive earlier in pregnancy but negative at the time of admission for labor and delivery were excluded from all analyses; 22 patients residing outside Massachusetts were excluded from any analysis assessing COVID-19 rate by zip code (Figure 1). Thirty-two out of 1,143 women tested positive for SARS-CoV-2 on admission; the risk of SARS-CoV-2 infection of patients tested in our sample was 2.8% (95% confidence interval [CI], 1.9-3.9). In Figure 2, new positive tests per capita in our study are compared to age-specific statewide data from the Massachusetts Department of Public Health by study week, with both populations showing a gradual decline in cases over the four-week study period.
Demographic and clinical factors strongly associated with SARS-CoV-2 infection include younger age (OR 4.01, 95% CI 1.55-10.41 for age <25 compared to age 25-35), obesity (OR 3.26, 95% CI 0.76-14.03 for delivery BMI > 30.0 kg/m2 compared to < 24.9 kg/m2), African American race (OR 6.54, 95% CI 1.96-21.85), and Hispanic ethnicity (OR 19.87, 95% CI 7.72-51.13) (Table 1; complete case analysis, Appendix 1). Geographic and occupational factors strongly associated with infection include an increased rate of documented SARS-CoV-2 infections per capita in the patient’s town (OR 26.85, 95% CI 7.86-91.66 for> 95th percentile compared to< 90th), a household member with known SARS-CoV-2 infection (OR 31.81, 95% CI 13.37-75.65), essential worker occupation excluding healthcare workers (OR 7.33, 95% CI 3.16-16.99), and Medicaid insurance vs. commercial (OR 10.87, 95% CI 5.14-22.98) (Table 2; complete case analysis, Appendix 1).
93.5% of women who tested positive at the time of admission for labor and delivery had at least one of these factors strongly associated with SARS-CoV-2 infection; 54.8% had four or more identifiable factors (Table 3, Figure 3). In contrast, only 5.8% of patients testing negative for SARS-CoV-2 had four or more factors associated with infection. While the number of outcome events precluded assessing the independent effect of each of these factors, the lasso regression identified COVID-19 rate in the 95th-99th percentile, Hispanic ethnicity, household member with known SARS-CoV-2 infection, and MassHealth or Medicaid insurance as the strongest predictors (Appendix 2). Among women testing positive on admission for labor and delivery, 75.0% were asymptomatic (Table 4).