Table 2. Adjusted Marginal Risk Differences for SARS-CoV-2 Infection and the COVID-19 Pandemic Period^a.

Outcome	R1b	R0c	RD (95% CI)d
COVID-19 pandemic period with SARS-CoV-2 infection (2020, n = 7150) vs COVID-19 pandemic period without SARS-CoV-2 infection (2020, n = 270 872)
Preterm birth	0.116	0.089	0.028 (0.021 to 0.035)
Spontaneous	0.084	0.064	0.020 (0.014 to 0.027)
Indicated	0.032	0.025	0.007 (0.004 to 0.011)
Hypertensive disorders of pregnancy	0.155	0.122	0.033 (0.024 to 0.041)
Gestational diabetes	0.121	0.114	0.007 (0.000 to 0.015)
Severe maternal morbidity	0.033	0.010	0.023 (0.019 to 0.027)
COVID-19 pandemic period without SARS-CoV-2 infection (2020, n = 270 872) vs prepandemic (2019, n = 300 030)
Preterm birth	0.085	0.089	−0.004 (−0.006 to −0.003)
Spontaneous	0.061	0.065	−0.004 (−0.005 to −0.003)
Indicated	0.024	0.024	0.000 (−0.001 to 0.000)
Hypertensive disorders of pregnancy	0.128	0.117	0.011 (0.009 to 0.012)
Gestational diabetes	0.121	0.112	0.009 (0.008 to 0.011)
Severe maternal morbidity	0.010	0.010	0.000 (−0.001 to 0.000)

^a Adjusted for birth parent’s age, race and ethnicity, insurance type, parity, education, and community characteristics (full list of variables and their categorization in Table 1). Parameters estimated with model-based standardization (g-computation) (eMethods in Supplement 1). Estimation with matching (generalized full matching) and targeted maximum likelihood estimation (TMLE) resulted in essentially equivalent results.

^b R1 is the estimated risk of the outcome if the exposed group (eg, group with SARS-CoV-2 infection) experienced the exposure, adjusted for covariates.

^c R0 is the estimated risk of the outcome if the exposed group had not experienced the exposure, adjusted for covariates.

^d RD is the risk difference R1 − R0, which estimates the amount of additional risk experienced by the exposed group (eg, group with SARS-CoV-2 infection, or COVID-19 pandemic period deliveries) that is associated with the exposure.