Table 1 Demographic characteristics of the study population

Maternal age (y)

Mean (SD)

34.5 (5.1)

35.2 (4.7)

32.4 (5.6)

 < 20

96 (0.1)

0 (0.0)

96 (0.2)

< 0.001

 20–34

97,874 (51.4)

66,789 (46.7)

31,085 (65.4)

 35 years or more

92,575 (48.6)

76,229 (53.3)

16,346 (34.4)

Maternal Race and Ethnicity

 Non-Hispanic white

140,375 (73.7)

107,436 (75.1)

32,939 (69.3)

< 0.001

 Non-Hispanic black

8,289 (4.4)

5,267 (3.7)

3,022 (6.4)

 Hispanic

16,166 (8.5)

8,682 (6.1)

7,484 (15.7)

 Non-Hispanic Other

24,539 (12.9)

20,734 (14.5)

3,805 (8.0)

 Unknown

1,176 (0.6)

899 (0.6)

277 (0.6)

Married

 No

12,962 (6.8)

7,165 (5.0)

5,797 (12.2)

< 0.001

 Yes

161,882 (85.0)

123,394 (86.3)

38,488 (81.0)

 Unknown

15,701 (8.2)

12,459 (8.7)

3,242 (6.8)

Insurance

 Medicaid

9,608 (5.0)

2,896 (2.0)

6,712 (14.1)

< 0.001

 Private

173,223 (90.9)

135,369 (94.7)

37,854 (79.6)

 Self-pay

2,449 (1.3)

1,605 (1.1)

844 (1.8)

 Other

4,607 (2.4)

2,747 (1.9)

1,860 (3.9)

 Unknown

658 (0.3)

401 (0.3)

257 (0.5)

Prenatal Care

 No

395 (0.2)

256 (0.2)

139 (0.3)

< 0.001

 Yes

187,065 (98.2)

140,453 (98.2)

46,612 (98.1)

 Unknown

3,085 (1.6)

2,309 (1.6)

776 (1.6)

Smoking during pregnancy

 No

189,045 (99.2)

142,566 (99.7)

46,479 (97.8)

< 0.001

 Yes

1,168 (0.6)

238 (0.2)

930 (2.0)

 Unknown

Pre-pregnancy BMI (kg/m²)

332 (0.2)

214 (0.1)

118 (0.2)

Mean (SD)

26.7 (10.2)

26.1 (10.1)

28.6 (10.5)

 Underweight (< 18.5)

4,605 (2.4)

3,665 (2.6)

940 (2.0)

< 0.001

 Normal weight (18.5–24.9)

98,989 (52.0)

80,701 (56.4)

18,288 (38.5)

 Overweight (25.0-29.9)

47,545 (25.0)

34,349 (24.0)

13,196 (27.8)

 Obesity I (30.0-34.9)

21,672 (11.4)

13,865 (9.7)

7,807 (16.4)

 Obesity II (35.0-39.9)

9,835 (5.2)

5,746 (4.0)

4,089 (8.6)

 Extreme Obesity III (≥ 40.0)

5,383 (2.8)

2,794 (2.0)

2,589 (5.4)

 Unknown

2,516 (1.3)

1,898 (1.3)

618 (1.3)

Prior preterm delivery

 No

185,139 (97.2)

139,412 (97.5)

45,727 (96.2)

< 0.001

 Yes

Gestational Age at Delivery

5,406 (2.8)

3,606 (2.5)

1,800 (3.8)

Mean (SD)

38.7 (1.9)

38.7 (1.9)

38.5 (2.1)

 24–36 weeks

15,748 (8.3)

11,254 (7.9)

4,494 (9.5)

 37–41 weeks

174,797 (91.7)

131,764 (92.1)

43,033 (90.5)

Infant sex

 Female

93,647 (49.1)

70,569 (49.3)

23,078 (48.6)

0.003

 Male

96,898 (50.9)

72,449 (50.7)

24,449 (51.4)

Route of delivery

 Cesarean

80,649 (42.3)

60,890 (42.6)

19,759 (41.6)

< 0.001

 Operative vaginal

10,183 (5.3)

7,952 (5.6)

2,231 (4.7)

 Spontaneous vaginal

99,671 (52.3)

74,145 (51.8)

25,526 (53.7)

 Unknown

42 (0.0)

31 (0.0)

11 (0.0)

Delivery year

 2016

33,051 (17.3)

24,343 (17.0)

8,708 (18.3)

< 0.001

 2017

36,607 (19.2)

27,421 (19.2)

9,186 (19.3)

 2018

38,713 (20.3)

29,039 (20.3)

9,674 (20.4)

 2019

41,278 (21.7)

31,081 (21.7)

10,197 (21.5)

 2020

40,896 (21.5)

31,134 (21.8)

9,762 (20.5)