Table 1.

Characteristics of women with a singleton birth in the Barnett Shale between 30 November 2010 and 29 November 2012 by preterm birth case status (cases, $n=\mathrm{13,549}$; controls, $n=\mathrm{67,745}$).

Characteristic	Cases n (%)	Controls n (%)
Maternal age in years, $\text{mean}\pm \text{SD}$	$27.5\pm 6.5$	$27.5\pm 6.4$
$<20$	2,218 (16.4)	11,090 (16.4)
21–25	3,359 (24.8)	16,795 (24.8)
26–30	3,436 (25.4)	17,180 (25.4)
31–35	2,787 (20.6)	13,935 (20.6)
$\ge 36$	1749 (12.9)	8,745 (12.9)
Race/ethnicity
Hispanic	5,137 (37.9)	25,685 (37.9)
Non-Hispanic white	4,514 (33.3)	22,570 (33.3)
Non-Hispanic black	3,083 (22.8)	15,415 (22.8)
Other	815 (6.0)	4,075 (6.0)
Prepregnancy BMI (${\mathrm{kg}/\mathrm{m}}^2$)
$<18.5$	620 (4.6)	2,519 (3.7)
18.5–24.9	6,642 (49.0)	34,733 (51.3)
25.0–29.9	2,984 (22.0)	15,657 (23.1)
30–34.9	1,780 (13.1)	8,330 (12.3)
$\ge 35.0$	1,414 (10.4)	6,133 (9.1)
Missing	109 (0.8)	373 (0.6)
Maternal education
$<\text{High}\text{school}$	3,038 (22.4)	14,322 (21.1)
High school graduate	4,484 (33.1)	20,869 (30.8)
Some college	3,460 (25.5)	17,077 (25.2)
College degree	2,550 (18.8)	15,442 (22.8)
Missing	17 ($<0.1$)	35 ($<0.1$)
Adequacy of prenatal care utilization
Inadequate	3,016 (22.3)	15,046 (22.2)
Intermediate	1,080 (8.0)	10,323 (15.2)
Adequate	2,590 (19.1)	28,724 (42.4)
Adequate plus	5,657 (41.8)	10,877 (16.1)
Unknown	1,206 (8.9)	2,775 (4.1)
Smoked during pregnancy
No	12,644 (93.3)	64,496 (95.2)
Yes	804 (5.9)	2,812 (4.2)
Missing	101 (0.7)	437 (0.6)
Previous poor pregnancy outcomea
No	13,251 (97.8)	66,635 (98.4)
Yes	298 (2.2)	1,110 (1.6)
Infant sex
Male	7,402 (54.6)	34,525 (51.0)
Female	6,147 (45.4)	33,220 (49.0)

Note: BMI, body mass index; SD, standard deviation.

^aIncludes previous preterm birth, small-for-gestational age, intrauterine growth restriction, and perinatal death/pregnancy termination.