Table 2. Comparison of maternal characteristics among pregnancies included and excluded from study.

Characteristic	Excluded N = 2,751		Included N = 12,526	p valuea
	n	%	%
Preterm (<37 weeks)	2,751	8.5	5.8	<0.0001
Age (years)	2,751
18–24		38.1	26.4	<0.0001
25–29		29.3	33.4
30–34		21.7	27.6
35–39		8.8	11.0
40+		2.1	1.7
Race/ethnicity	2,663			<0.0001
Non-Hispanic White		69.6	74.4
Non-Hispanic Black		3.8	2.3
Hispanic		11.3	7.4
Asian/Pacific Islander		4.7	3.9
Other/Unknown/Mixed		10.6	12.0
Education (years)	2,495			<0.0001
<12		10.5	5.9
12		32.6	23.2
>12		57.0	70.9
Enrolled in Medicaid or Washington basic health plan	2,751	9.6	4.1	<0.0001
Parity	2,553			<0.0001
0		42.6	46.9
1+		57.4	53.1
Used tobacco during pregnancy	2,482	13.7	9.0	<0.0001
Diagnosed with pre-gestational or gestational diabetes mellitus	2,751	5.4	5.2	0.74
Diagnosed with any hypertensive disorder during pregnancy	2,750	8.6	8.7	0.80

^ap value based on χ²