Table 1 Characteristics of the study population

N

12144972

11011647

1130017

11295453

846288

11417309

724008

11433236

687173

Maternal age at delivery, years

Median (interquartile range)

29 (25–33)

29 (25–33)

27 (23–31)

< 0.0001

29 (25–33)

27 (23–31)

< 0.0001

29 (25–33)

27 (23–31)

< 0.0001

29 (25–33)

27 (23–31)

< 0.0001

Category, n (%)

< 0.0001

< 0.0001

< 0.0001

< 0.0001

18–29

6633206 (54.6)

5853770 (53.2)

777222 (68.8)

6051459 (53.6)

579567 (68.5)

6139155 (53.8)

491571 (67.9)

6153808 (53.8)

465025 (67.7)

30–39

5158070 (42.5)

4821115 (43.8)

335908 (29.7)

4903379 (43.4)

253694 (30.0)

4935865 (43.2)

221082 (30.5)

4937444 (43.2)

211273 (30.8)

40–49

353696 (2.9)

336762 (3.1)

16887 (1.5)

340615 (3.0)

13027 (1.5)

342289 (3.0)

11355 (1.6)

341984 (3.0)

10875 (1.6)

Race/ethnicity, n (%)

< 0.0001

< 0.0001

< 0.0001

< 0.0001

Hispanic

2594603 (21.4)

2515412 (22.8)

78738 (7.0)

2546720 (22.6)

47554 (5.6)

2557944 (22.4)

36268 (5.0)

2556280 (22.4)

33474 (4.9)

Non-Hispanic white

6702736 (55.2)

5843582 (53.1)

857114 (75.9)

6044060 (53.5)

656548 (77.6)

6129954 (53.7)

570408 (78.8)

6149206 (53.8)

543958 (79.2)

Non-Hispanic black

1773802 (14.6)

1648063 (15.0)

125290 (11.1)

1681172 (14.9)

92231 (10.9)

1697196 (14.9)

76148 (10.5)

1694668 (14.8)

71043 (10.3)

Other

1073831 (8.8)

1004590 (9.1)

68875 (6.1)

1023501 (9.1)

49955 (5.9)

1032215 (9.0)

41184 (5.7)

1033082 (9.0)

38698 (5.6)

Education level, n (%)

< 0.0001

< 0.0001

< 0.0001

< 0.0001

Less than high school

1446923 (11.9)

1212753 (11.0)

233557 (20.7)

1246992 (11.0)

199297 (23.6)

1265771 (11.1)

180425 (24.9)

1269412 (11.1)

173981 (25.3)

High school

3138189 (25.8)

2665352 (24.2)

471540 (41.7)

2770947 (24.5)

366018 (43.3)

2820303 (24.7)

316486 (43.7)

2828893 (24.7)

300653 (43.8)

More than high school

7559860 (62.3)

7133542 (64.8)

424920 (37.6)

7277514 (64.4)

280973 (33.2)

7331235 (64.2)

227097 (31.4)

7334931 (64.2)

212539 (30.9)

Marital status, n (%)

< 0.0001

< 0.0001

< 0.0001

< 0.0001

Married

7413803 (61.0)

7077878 (64.3)

334872(29.6)

7183325 (63.6)

229352 (27.1)

7217956 (63.2)

194619 (26.9)

7217754 (63.1)

185756 (27.0)

Unmarried

4731169 (39.0)

3933769 (35.7)

795145(70.4)

4112128 (36.4)

616936 (72.9)

4199353 (36.8)

529389 (73.1)

4215482 (36.9)

501417 (73.0)

Maternal pre-pregnancy BMI, n (%)

< 0.0001

< 0.0001

< 0.0001

< 0.0001

< 18.5

398617 (3.3)

338266 (3.1)

60219 (5.3)

349638 (3.1)

48847 (5.8)

355457 (3.1)

43016 (5.9)

356831 (3.1)

40934 (6.0)

18.5–24.9

5258272 (43.3)

4808587 (43.7)

448405 (39.7)

4915778 (43.5)

341196 (40.3)

4962552 (43.5)

294233 (40.6)

4970360 (43.5)

279659 (40.7)

25.0–29.9

3226439 (26.6)

2947167 (26.8)

278406 (24.6)

3020845 (26.7)

204767 (24.2)

3051195 (26.7)

174315 (24.1)

3054557 (26.7)

165555 (24.1)

30.0–-34.9

1793991 (14.8)

1615555 (14.7)

177896 (15.7)

1663012 (14.7)

130475 (15.4)

1683067 (14.7)

110357 (15.2)

1685008 (14.7)

104585 (15.2)

35.0–39.9

869844 (7.2)

774057 (7.0)

95506 (8.5)

799561 (7.1)

70016 (8.3)

810359 (7.1)

59176 (8.2)

811208 (7.1)

55947 (8.1)

≥ 40

597809 (4.9)

528015 (4.8)

69585 (6.2)

546619 (4.8)

50987 (6.0)

554679 (4.9)

42911 (5.9)

555272 (4.9)

40493 (5.9)

Eclampsia, n (%)

30111 (0.3)

27230 (0.3)

2873 (0.3)

0.1565

28016 (0.3)

2076 (0.3)

0.6271

28342 (0.3)

1746 (0.2)

0.2400

28271 (0.3)

1624 (0.2)

0.0758

Gestational hypertension, n (%)

828884 (6.8)

747722 (6.8)

80863 (7.2)

< 0.0001

771842 (6.8)

56769 (6.7)

< 0.0001

782007 (6.9)

46563 (6.4)

< 0.0001

783133 (6.9)

43423 (6.3)

< 0.0001

Gestational diabetes, n (%)

766668 (6.3)

697156 (6.3)

69284 (6.1)

< 0.0001

717261 (6.4)

49195 (5.8)

< 0.0001

725557 (6.4)

40868 (5.6)

< 0.0001

727192 (6.4)

38653 (5.6)

< 0.0001

Parity, n (%)

< 0.0001

1

4604618 (37.9)

4226115 (38.4)

377146 (33.4)

4359594 (38.6)

243802 (28.8)

4412457 (38.7)

190769 (26.4)

4416750 (38.6)

176170 (25.6)

2

3941322 (32.5)

3605704 (32.7)

334684 (29.6)

3688377 (32.7)

251985 (29.8)

3723521 (32.6)

216701 (29.9)

3729275 (32.6)

205941 (30.0)

3

2089008 (17.2)

1864709 (16.9)

223754 (19.8)

1906643 (16.9)

181789 (21.5)

1926676 (16.9)

161710 (22.3)

1930274 (16.9)

155298 (22.6)

≥4

1510024 (12.4)

1315119 (11.9)

194433 (17.2)

1340839 (11.9)

168712 (19.9)

1354655 (11.9)

154828 (21.4)

1356937 (11.9)

149764 (21.8)

Infant sex, n (%)

0.4854

0.3737

0.1427

0.2976

Male

6212985 (51.2)

5633535 (51.2)

577725 (51.1)

5777992 (51.2)

433328 (51.2)

5840111 (51.2)

370983 (51.2)

5847928 (51.2)

351923 (51.2)

Female

5931987 (48.8)

5378112 (48.8)

552292 (48.9)

5517461 (48.9)

412960 (48.8)

5577198 (48.9)

353025 (48.8)

5585308 (48.9)

335250 (48.8)

Gestational age at delivery, weeks, median (interquartile range)

39 (38–40)

39 (38–40)

39 (38–39)

< 0.0001

39 (38–40)

39 (38–39)

< 0.0001

39 (38–40)

39 (38–39)

< 0.0001

39 (38–40)

39 (38–39)

< 0.0001

Total number of prenatal care visits, n (%)

< 0.0001

< 0.0001

< 0.0001

< 0.0001

0

192355 (1.6)

157685 (1.4)

34613 (3.1)

160767 (1.4)

31511 (3.7)

162638 (1.4)

29629 (4.1)

161541 (1.4)

28498 (4.2)

1–4

453702 (3.7)

374231 (3.4)

79251 (7.0)

384157 (3.4)

69312 (8.2)

390034 (3.4)

63413 (8.8)

385657 (3.4)

60258 (8.8)

5–9

2511582 (20.7)

2230669 (20.3)

280034 (24.8)

2287074 (20.3)

223700 (26.4)

2314457 (20.3)

196206 (27.1)

2315802 (20.3)

186173 (27.1)

≥ 10

8987333 (74.0)

8249062 (74.9)

736119 (65.1)

8463455 (74.9)

521765 (61.7)

8550180 (74.9)

434760 (60.1)

8570236 (75.0)

412244 (60.0)