Table 1 Changes in population characteristics and small-for-gestational age (SGA) rates in the United States 1990–1992, 2002–2004, 2008–2010

Age <20 years

1,266,799 (13.1)

178,826 (14.1)

1,088,005 (10.8)

143,644 (13.2)

1,190,869 (10.1)

156,115 (13.1)

 20–24 years

2,565,257 (26.6)

285,798 (11.1)

2,611,711 (25.9)

272,080 (10.4)

2,900,487 (24.6)

307,631 (10.6)

 25–29 years

2,890,561 (29.9)

260,847 (9.0)

2,699,395 (26.8)

214,646 (8.0)

3,346,378 (28.4)

279,361 (8.3)

 30–34 years

2,069,631 (21.4)

174,713 (8.4)

2,345,977 (23.3)

162,548 (6.9)

2,721,282 (23.1)

202,789 (7.5)

 35–39 years

747,403 (7.7)

66,494 (8.9)

1,097,056 (10.9)

82,088 (7.5)

1,335,357 (11.3)

101,957 (7.6)

 ≥40 years

117,194 (1.2)

11,932 (10.2)

239,552 (2.4)

21,858 (9.1)

311,398 (2.6)

27,668 (8.9)

Non-Hispanic White

6,636,243 (68.7)

540,896 (8.2)

6,132,920 (60.8)

438,101 (7.1)

6,359,020 (53.9)

471,413 (7.4)

Non-Hispanic Black

1,700,294 (17.6)

291,888 (17.2)

1,559,920 (15.5)

231,876 (14.9)

1,731,740 (14.7)

262,800 (15.2)

Hispanic

992,365 (10.3)

106,957 (10.8)

1,857,538 (18.4)

167,041 (9.0)

2,901,453 (24.6)

248,242 (8.6)

Other

327,943 (3.4)

38,869 (11.9)

531,318 (5.3)

59,846 (11.3)

813,558 (6.9)

93,066 (11.4)

Low education

2,007,942 (21.7)

289,581 (14.4)

2,061,474 (20.7)

246,226 (11.9)

2,340,804 (20.1)

266,128 (11.4)

Mother not married

2,756,978 (28.6)

416,329 (15.1)

3,548,727 (35.2)

434,968 (12.3)

4,850,493 (41.1)

568,102 (11.7)

Maternal smoking

1,504,155 (17.7)

264,893 (17.6)

1,112,652 (11.3)

174,247 (15.7)

984,727 (9.5)

156,269 (15.9)

Nulliparous

3,160,790 (32.9)

368,815 (11.7)

3,339,247 (33.3)

365,533 (10.9)

4,000,839 (34. 3)

450,705 (11.3)

Nulliparous, ≥35 years

118,162 (1.2)

14,550 (12.3)

209,556 (2.1)

22,694 (10.8)

266,465 (2.3)

29,673 (11.1)

Labour induced

1,097,842 (11.4)

99,493 (9.1)

2,315,760 (23.0)

199,300 (8.6)

2,800,695 (23.7)

263,567 (9.4)

Cesarean delivery

2,100,393 (21.8)

216,111 (10.3)

2,631,066 (26.1)

248,880 (9.5)

3,674,107 (31.1)

349,172 (9.5)

Infant sex (male)

4,942,269 (51.2)

397,264 (8.0)

5,160,195 (51.2)

359,953 (7.0)

6,042,020 (51.2)

427,464 (7.1)

Gest. age <32 weeks

106,575 (1.1)

7926 (7.4)

112,312 (1.1)

10,745 (9.6)

125,037 (1.1)

12,083 (9.7)

 32–33 weeks

82,200 (0.9)

11,889 (14.5)

91,770 (0.9)

14,557 (15.9)

102,715 (0.9)

17,192 (16.7)

 34–36 weeks

478,843 (5.0)

77,605 (16.2)

637,780 (6.3)

90,439 (14.2)

721,151 (6.1)

105,742 (14.7)

 37–38 weeks

1,721,215 (17.8)

206,315 (12.0)

2,763,381 (27.4)

262,380 (9.5)

3,339,299 (28.3)

337,035 (10.1)

 39–40 weeks

5,712,036 (59.2)

580,887 (10.2)

5,581,621 (55.4)

470,764 (8.4)

6,698,762 (56.7)

559,528 (8.4)

 41 weeks

1,160,789 (12.0)

73,403 (6.3)

805,794 (8.0)

43,635 (5.4)

760,526 (6.4)

40,911 (5.4)

 ≥42 weeks

395,187 (4.1)

20,585 (5.2)

89,038 (0.9)

4344 (4.9)

58,281 (0.5)

3030 (5.2)

Total

9,656,845 (100)

978,610 (10.1)

10,081,696 (100)

896,864 (8.9)

11,805,771 (100)

1,075,521 (9.1)