Table 1.

Demographics of singleton births and distribution of term birth weight and term small for gestational age among 403 U.S. counties from 1989 to 2002.

Variable	Count (%)	Term mean birth weight (g) ($\text{mean}\pm \text{SD}$)	Term SGA (%)
Total birth	29,597,735 (100.0)	$\mathrm{3,436}\pm 482$	10.2
Child sex
Male	15,071,495 (50.9)	$\mathrm{3,499}\pm 487$	10.1
Female	14,526,240 (49.1)	$\mathrm{3,371}\pm 467$	10.2
Parity
0	12,339,520 (41.7)	$\mathrm{3,386}\pm 473$	12.2
1	9,564,292 (32.3)	$\mathrm{3,471}\pm 474$	8.4
$\ge 2$	7,588,896 (25.6)	$\mathrm{3,474}\pm 497$	9.2
Unknown	105,027 (0.4)	$\mathrm{3,402}\pm 484$	11.6
Maternal age (y)
$<25$	10,027,881 (33.9)	$\mathrm{3,360}\pm 470$	13.2
25–29	8,491,989 (28.7)	$\mathrm{3,456}\pm 476$	9.2
30–34	7,324,962 (24.7)	$\mathrm{3,490}\pm 482$	8.1
$\ge 35$	3,752,903 (12.7)	$\mathrm{3,491}\pm 498$	8.4
Marital status
Married	20,779,953 (70.2)	$\mathrm{3,479}\pm 475$	8.2
Unmarried	8,817,782 (29.8)	$\mathrm{3,335}\pm 481$	14.7
Maternal race
White	23,329,456 (78.8)	$\mathrm{3,475}\pm 476$	8.5
Nonwhite	6,268,279 (21.2)	$\mathrm{3,291}\pm 474$	16.1
Maternal education (y)
$<9$	1,885,775 (6.4)	$\mathrm{3,409}\pm 479$	11.3
9–12	13,460,319 (45.5)	$\mathrm{3,390}\pm 485$	12.3
13–17	13,529,645 (45.7)	$\mathrm{3,486}\pm 473$	7.8
Unknown	721,996 (2.4)	$\mathrm{3,439}\pm 490$	10.5
Smoking during pregnancya
Yes	2,577,131 (8.7)	$\mathrm{3,260}\pm 481$	19.1
No	19,155,778 (64.7)	$\mathrm{3,455}\pm 477$	9.1
Unknown	7,864,826 (26.6)	$\mathrm{3,449}\pm 481$	9.7
Alcohol drinking during pregnancya
Yes	384,220 (1.3)	$\mathrm{3,351}\pm 521$	16.2
No	22,176,203 (74.9)	$\mathrm{3,434}\pm 481$	10.2
Unknown	7,037,312 (23.8)	$\mathrm{3,447}\pm 480$	9.7
Chronic hypertension
Yes	167,815 (0.6)	$\mathrm{3,342}\pm 555$	15.5
No	28,833,979 (97.4)	$\mathrm{3,437}\pm 481$	10.1
Unknown	595,941 (2.0)	$\mathrm{3,432}\pm 489$	10.7
Season of conceptionb
Spring	6,916,145 (23.4)	$\mathrm{3,431}\pm 483$	10.5
Summer	7,456,193 (25.2)	$\mathrm{3,446}\pm 482$	9.8
Fall	7,679,851 (25.9)	$\mathrm{3,436}\pm 481$	10.1
Winter	7,545,546 (25.5)	$\mathrm{3,432}\pm 480$	10.2
Geographic region
Northeast	7,605,824 (25.7)	$\mathrm{3,444}\pm 485$	10.1
Southeast	4,807,500 (16.2)	$\mathrm{3,408}\pm 484$	11.3
Midwest	5,788,152 (19.6)	$\mathrm{3,447}\pm 487$	10.1
Great Plains	3,158,660 (10.7)	$\mathrm{3,417}\pm 472$	10.3
Northwest	952,436 (3.2)	$\mathrm{3,512}\pm 481$	7.7
Southwest	7,285,163 (24.6)	$\mathrm{3,437}\pm 475$	9.8
Climate zone
Hot-humid	4,592,942 (15.5)	$\mathrm{3,410}\pm 477$	10.8
Mixed-humid	7,699,893 (26.0)	$\mathrm{3,419}\pm 485$	10.9
Hot-dry/mixed-dry	5,432,313 (18.4)	$\mathrm{3,440}\pm 475$	9.7
Cold/very cold	9,890,639 (33.4)	$\mathrm{3,450}\pm 483$	9.8
Marine	1,981,948 (6.7)	$\mathrm{3,487}\pm 481$	8.4

Note: SD, standard deviation; SGA, small for gestational age.

^aSmoking and drinking status were not recorded on California birth certificate.

^bSeason of conception: spring (March–May), summer (June–August), fall (September–November), and winter (December–February).