Table 4.

Logistic regression analysis predicting postnatal Early Check enrollments among North or South Carolina residents who gave birth in North Carolina from September 17, 2018, through March 19, 2019, by phase I outreach method, urbanicity, estimated race and ethnicity, and Early Check birth hospital affiliation

Predictor	OR	SE	p	95% CI
				LL	UL
Letter (reference = Not sent a recruitment letter)
Sent a recruitment letter	39.07	23.01	<0.001	12.32	123.95
Email (reference = Not sent an email invitation)
Sent a personalized email invitation	1.33	0.10	<0.001	1.14	1.55
Postcard (reference = Not sent a reminder postcard)
Sent a reminder postcard	0.98	0.08	0.802	0.83	1.15
Urbanicity (reference = Rural)
Urban	1.48	0.11	<0.001	1.29	1.71
Race/ethnicity (reference = White)
Black	0.99	0.00	<0.001	0.99	0.99
American Indian	0.99	0.00	0.023	0.99	1.00
Hispanic	0.99	0.00	<0.001	.99	1.00
Other	1.00	0.00	0.141	1.00	1.01
Birth hospital affiliation (reference = Not affiliated)
Affiliated with an Early Check research partner	1.68	0.10	<0.001	1.50	1.89
State of residence (reference = South Carolina)
North Carolina	0.84	0.11	0.191	0.65	1.09
Baby’s date of birth	1.00	0.00	0.237	1.00	1.00
Number of days enrollment window crossed into phase II	1.01	0.00	<0.001	1.01	1.02
Number of days permission portal unavailable	1.01	0.01	0.241	0.99	1.02
Additional days postnatal enrollment window	0.94	.03	0.083	0.89	1.01
Constant	0.00	.00	0.152

Log‐likelihood = −9060.03, χ²(14) = 339.93, p < 0.001, R² _McFadden’s = 0.03. N = 56,398. The analysis excluded 21 women for whom geolocation data were insufficient to compute urbanicity and 38 women who enrolled their children prenatally. In the case of multiple births and repeat samples, we used location data from the earliest record for each mother.

CI, confidence interval; LL, lower limit of the 95% CI; OR, odds ratio; SE, robust standard errors that allow for clustering by census tracts; UL, upper limit of the 95% CI.