Table 1 The characteristic of the population

2016–2018

10,900,495

10,749,487 (98.6)

151,008 (1.4)

Years

 < .001

 2016

3,716,502 (34.1)

3,670,624 (34.1)

45,878 (30.4)

 2017

3,622,835 (33.2)

3,572,006 (33.2)

50,829 (33.6)

 2018

3,561,158 (32.7)

3,506,875 (32.7)

54,301 (36.0)

Maternal age, Mean (SD)

28.7 ± 5.8

28.7 ± 5.8

34.4 ± 5.3

 < .001

Maternal age

  < 20

573,141 (5.3)

559,166 (5.2)

13,975 (8.0)

 20–24

2,201,632 (20.2)

2,159,825 (20.1)

41,807 (24.0)

 25–29

3,195,106 (29.3)

3,143,691 (29.3)

51,415 (29.5)

 30–34

3,076,362 (28.2)

3,031,396 (28.3)

44,966 (25.8)

  ≥ 35

1,854,254 (17.0)

1,832,054 (17.1)

22,200 (12.7)

Race and ethnicity

 < .001

 White

5,637,228 (51.7)

5,527,876 (51.4)

109,352 (72.4)

 Black

1,523,114 (14.0)

1,516,357 (14.1)

6,757 (4.5)

 AIAN

83,809 (0.8)

83,554 (0.8)

255 (0.2)

 Asia

709,461 (6.5)

692,825 (6.4)

16,636 (11.0)

 NHOPI

26,599 (0.2)

26,512 (0.2)

87 (0.1)

  > 1race

231,508 (2.1)

247,238 (2.3)

2,265 (1.5)

 Hispanic

2,595,187 (23.8)

2,582,707 (24.0)

12,480 (8.3)

 Unknown

93,589 (0.9)

90,579 (0.8)

3,010 (2.0)

Education

 < .001

  < 8^th grade

356,492 (3.3)

355,975 (3.3)

517 (0.3)

 9–12^th grade without diploma

1,085,317 (10.0)

1,083,872 (10.1)

1,445 (1.0)

 High school

2,752,395 (25.2)

2,742,444 (25.5)

9,951 (6.6)

 College or above degree

6,568,372 (60.2)

6,432,282 (59.8)

136,090 (90.1)

 Unknown

137,919 (1.3)

134,914 (1.3)

3,005 (2.0)

Marital status

 < .001

 Married

6,009,650 (55.2)

5,879,998 (54.7)

129,652 (85.9)

 Unmarried

4,005,815 (36.7)

3,995,119 (37.2)

10,696 (7.1)

 Unknown

885,030 (8.1)

874,370 (8.1)

10,660 (7.0)

Parity

 < .001

 1

3,435,120 (31.5)

3,371,324 (31.4)

63,796 (42.2)

 2

3,072,417 (28.2)

3,031,620 (28.2)

40,797 (27.0)

 3–7

4,165,274 (38.2)

4,120,685 (38.3)

44,589 (29.5)

  ≥ 8

182,477 (1.7)

180,990 (1.7)

1,487 (1.0)

 Unknown

45,207 (0.4)

44,868 (0.4)

339 (0.2)

Pre-pregnancy BMI, (kg/m², Mean ± SD)

26.8 ± 6.5

26.8 ± 6.5

26.3 ± 6.2

 < .001

Pre-pregnancy BMI (kg/m²)

 < .001

  < 18.5

367,097 (3.4)

363,669 (3.4)

3,428 (2.3)

 18.5–24.9

4,689,671 (43.0)

4,616,709 (42.9)

72,908 (48.3)

 25–29.9

2,808,007 (25.8)

2,770,212 (25.8)

37,795 (25.0)

 30–34.9

1,538,729 (14.1)

1,519,608 (14.1)

19,121 (12.7)

 35–39.9

733,717 (6.7)

1,724,168 (6.7)

9,549 (6.3)

  ≥ 40

495,830 (4.5)

490,045 (4.6)

5,785 (3.8)

 Unknown

267,498 (2.5)

265,076 (2.5)

2,422 (1.6)

Weight gain (pounds, Mean ± SD)

29.5 ± 14.9

29.5 ± 14.9

29.9 ± 13.5

 < .001

Weight gain (pounds)

  < 11

1,010,668 (9.3)

999,935 (9.3)

10,733 (7.1)

 11–20

1,842,421 (16.9)

1,818,969 (16.9)

23,452 (15.5)

 21–30

3, 027,782 (27.7)

2,981,498 (27.7)

46,284 (30.7)

 31–39

2,571,361 (23.6)

2,531,022 (23.6)

40,339 (26.7)

  ≥ 40

2,091,552 (19.2)

2,064,705 (19.2)

26,847 (17.8)

 Unknown

356,711 (3.3)

353,358 (3.3)

3,353 (2.2)

Smoking status

 Pre-pregnancy

 < .001

  No

9,887,874 (90.7)

9,739,703 (90.6)

148,171 (98.1)

  Yes

961,293 (8.8)

958,732 (8.9)

2,561 (1.7)

  Unknown

51,328 (0.5)

51,051 (0.5)

276 (0.2)

 1^st trimester

 < .001

  No

1,0129,738 (92.9)

9,980,158 (92.8)

149,580 (99.1)

  Yes

719,989 (6.6)

718,837 (6.7)

1,152 (0.7)

  Unknown

50,768 (0.5)

50,492 (0.5)

276 (0.2)

 2^nd trimester

 < .001

  No

10,233,710 (93.9)

10,083,901 (93.8)

149,809 (99.2)

  Yes

615,413 (5.6)

614,493 (5.7)

920 (0.6)

  Unknown

51,372 (0.5)

51,093 (0.5)

279 (0.2)

 3^rd trimester

 < .001

  No

10,250,606 (94.0)

10,101,156 (94.0)

149,450 (99.0)

  Yes

584,163 (5.4)

583,282 (5.4)

881 (0.6)

  Unknown

65,726 (0.6)

65,049 (0.6)

677 (0.4)

Time of initiation of prenatal care

 < .001

 1^st trimester

8,190,475 (75.1)

8, 057,090 (75.0)

13,385 (88.3)

 2^nd trimester

1,759,978 (16.1)

1,747,559 (16.1)

12,419 (8.3)

 3^rd trimester

492,141 (4.6)

489,857 (4.6)

2,284 (1.5)

 No

178,189 (1.6)

177,896 (1.7)

293 (0.2)

 Unknown

279,712 (2.6)

277,085 (2.6)

2,627 (1.7)

Prenatal visit (times)

 < .001

 No

178,189 (1.6)

177,896 (1.7)

293 (0.2)

 1–8

1,893,391 (17.4)

1,878,128 (17.5)

15,263 (10.1)

 9–12

4,974,243 (45.6)

4,905,661 (45.6)

68,582 (45.4)

 13–16

2,949,575 (27.1)

2,900,909 (27.0)

48,666 (32.2)

  ≥ 16

627,812 (5.8)

612,543 (5.7)

15,269 (10.1)

 Unknown

277,285 (2.5)

274,350 (2.5)

2,935 (2.0)

WIC

 < .001

 No

6,700,937 (61.5)

6,560,267 (61.0)

140,670 (93.2)

 Yes

4,073,947 (37.3)

4,065,306 (37.8)

8,641 (5.7)

 Unknown

125,611 (1.2)

123,914 (1.2)

1,697 (1.1)

Payment

 < .001

 Medicaid

4,616,354 (42.3)

4,607,743 (42.9)

8,611 (5.7)

 Private

5,327,063 (48.9)

5,191,526 (48.3)

135,537 (89.8)

 Self-pay

473,387 (4.3)

470,669 (4.3)

2,718 (1.8)

 Other

419,905 (3.9)

416,385 (3.9)

3,520 (2.3)

 Unknown

63,786 (0.6)

63,164 (0.6)

622 (0.4)

Gestational diabetes

 < .001

 No

10,233,331 (93.9)

10,097,926 (93.9)

135,405 (89.7)

 Yes

667,164 (6.1)

651,561 (6.1)

15,603 (10.3)

Gestational hypertension

 < .001

 No

10,212,180 (93.7)

10,076,444 (93.7)

135,736 (89.9)

 Yes

688,315 (6.3)

673,043 (6.3)

15,272 (10.1)

Eclampsia

 < .001

 No

10,875,230 (99.8)

10,724,672 (99.8)

150,558 (99.7)

 Yes

25,265 (0.2)

24,815 (0.2)

450 (0.3)

History of preterm birth

0.389

 No

10,563,932 (96.9)

10,417,529 (96.9)

146,403 (97.0)

 Yes

336,563 (3.1)

331,958 (3.1)

4,605 (3.0)

History of cesarean

 < .001

 No

9,246,679 (84.8)

9,115,508 (84.8)

131,171 (86.9)

 Yes

1,652,813 (15.2)

1,633,979 (15.2)

19,837 (13.1)

Infection

 Gonorrhea

 < .001

  No

10,869,158 (99.7)

10,718,199 (99.7)

150,959 (100.0)

  Yes

31,337 (0.3)

31,288 (0.3)

49 (0.0)

 Syphilis

 < .001

  No

10,889,768 (99.9)

10,738,805 (99.9)

150,963 (100.0)

  Yes

10,727 (0.1)

10,628 (0.1)

45 (0.0)

 Chlamydia

 < .001

  No

10,700,001 (98.2)

10,549,378 (98.1)

150,623 (99.7)

  Yes

200,494 (1.8)

200,109 (1.9)

385 (0.3)

 Hepatitis B

.009

  No

10,876,011 (99.8)

10 725 390 (99.8)

150 621 (99.7)

  Yes

24,484 (0.2)

24 097 (0.2)

387 (0.3)

 Hepatitis C

 < .001

  No

10,850,932 (99.5)

10,700,040 (99.5)

150,892 (99.9)

  Yes

49,563 (0.5)

49,447 (0.5)

116 (0.1)

Neonatal sex

0.458

 Female

5,322,388 (48.8)

5,248,512 (48.8)

73,876 (48.9)

 Male

5,578,107 (51.2)

5,500,975 (51.2)

77,132 (51.1)

Chorioamnionitis

 < .001

 No

10,726,132 (98.4)

10,579,714 (98.4)

146,418 (97.0)

 Yes

174,363 (1.6)

169,773 (1.6)

4,590 (3.0)