Table 1 Maternal and neonatal characteristics

Maternal age at delivery, years, Mean ± SD

29.61 ± 5.54

29.53 ± 5.50

35.84 ± 4.87

Age subgroups, n (%)

<35 years

2,263,460 (80.14)

2,249,290 (80.64)

14,170 (40.46)

≥35years

560,958 (19.86)

540,108 (19.36)

20,850 (59.54)

Race of mother, n (%)

White

2,156,689 (76.36)

2,129,552 (76.34)

27,137 (77.49)

Black

357,342 (12.65)

355,554 (12.75)

1,788 (5.11)

Others

105,102 (3.72)

104,379 (3.74)

723 (2.06)

Asian

205,285 (7.27)

199,913 (7.17)

5,372 (15.34)

Educational level of mother, n (%)

Less than high school

81,575 (2.89)

81,475 (2.92)

100 (0.29)

High school

859,126 (30.42)

857,181 (30.73)

1,945 (5.55)

Bachelor or above

1,849,939 (65.50)

1,818,076 (65.18)

31,863 (90.99)

Unknown

33,778 (1.20)

32,666 (1.17)

1,112 (3.18)

Marital status, n (%)

Unmarried

789,496 (27.95)

788,170 (28.26)

1,326 (3.79)

Married

1,677,120 (59.38)

1,648,773 (59.11)

28,347 (80.95)

Unknown

357,802 (12.67)

352,455 (12.64)

5,347 (15.27)

Age of father, years, Mean ± SD

31.95 ± 6.67

31.87 ± 6.64

38.13 ± 6.39

Race of father, n (%)

White

1,942,863 (68.79)

1,916,519 (68.71)

26,344 (75.23)

Black

388,297 (13.75)

386,438 (13.85)

1,859 (5.31)

Other

95,417 (3.38)

94,760 (3.40)

657 (1.88)

Asian

174,795 (6.19)

170,426 (6.11)

4,369 (12.48)

Unknown

223,046 (7.90)

221,255 (7.93)

1,791 (5.11)

Educational level of father, n (%)

Less than high school

99,839 (3.53)

99,710 (3.57)

129 (0.37)

High school

1,050,212 (37.18)

1,046,720 (37.52)

3,492 (9.97)

Bachelor or above

1,602,222 (56.73)

1,572,117 (56.36)

30,105 (85.97)

Unknown

72,145 (2.55)

70,851 (2.54)

1,294 (3.70)

Smoking before pregnancy, n (%)

No

2,667,141 (94.43)

2,632,337 (94.37)

34,804 (99.38)

Yes

157,277 (5.57)

157,061 (5.63)

216 (0.62)

Smoking during pregnancy, n (%)

No

2,706,508 (95.83)

2,671,586 (95.78)

34,922 (99.72)

Yes

117,910 (4.17)

117,812 (4.22)

98 (0.28)

Total number of prenatal care visits for this pregnancy, number, M (Q₁, Q₃)

11.00 (9.00, 13.00)

11.00 (9.00, 13.00)

12.00 (10.00, 14.00)

Pre-pregnancy BMI, kg/m², Mean ± SD

27.24 ± 6.57

27.25 ± 6.58

26.02 ± 5.70

Pre-pregnancy chronic diabetes, n (%)

No

2,799,766 (99.13)

2,765,091 (99.13)

34,675 (99.01)

Yes

24,652 (0.87)

24,307 (0.87)

345 (0.99)

Gestational diabetes, n (%)

No

2,603,840 (92.19)

2,572,908 (92.24)

30,932 (88.33)

Yes

220,578 (7.81)

216,490 (7.76)

4,088 (11.67)

Gestational hypertension, n (%)

No

2,590,390 (91.71)

2,559,677 (91.76)

30,713 (87.70)

Yes

234,028 (8.29)

229,721 (8.24)

4,307 (12.30)

Eclampsia, n (%)

No

2,817,716 (99.76)

2,782,794 (99.76)

34,922 (99.72)

Yes

6,702 (0.24)

6,604 (0.24)

98 (0.28)

PIH, n (%)

No

2584,830 (91.52)

2,554,194 (91.57)

30,636 (87.48)

Yes

239,588 (8.48)

235,204 (8.43)

4,384 (12.52)

Clinical chorioamnionitis or maternal fever during labor, n (%)

No

2,779,538 (98.41)

2,745,595 (98.43)

33,943 (96.92)

Yes

44,880 (1.59)

43,803 (1.57)

1,077 (3.08)

Previous preterm births, n (%)

No

2,733,365 (96.78)

2,699,434 (96.77)

33,931 (96.89)

Yes

91,053 (3.22)

89,964 (3.23)

1,089 (3.11)

Previous cesarean section, n (%)

No

2,389,278 (84.59)

2,359,606 (84.59)

29,672 (84.73)

Yes

435,140 (15.41)

429,792 (15.41)

5,348 (15.27)

Parity, n (%)

Primipara

1,095,213 (38.78)

1,075,044 (38.54)

20,169 (57.59)

Multipara

1,729,205 (61.22)

1,714,354 (61.46)

14,851 (42.41)

Gestational weight gain, pounds, M (Q₁, Q₃)

29.00 (20.00, 38.00)

29.00 (20.00, 38.00)

29.00 (21.00, 37.00)

Gestational age, weeks, Mean ± SD

38.75 ± 1.97

38.75 ± 1.96

38.54 ± 2.17

Adverse neonatal outcomes, n (%)

No

2,399,677 (84.96)

2,371,792 (85.03)

27,885 (79.63)

Yes

424,741 (15.04)

417,606 (14.97)

7,135 (20.37)

Neonatal weight, g, Mean ± SD

3,324.07 ± 521.64

3,324.12 ± 521.27

3,320.24 ± 549.90

Low birth weight, n (%)

No

2,672,002 (94.60)

2,639,294 (94.62)

32,708 (93.40)

Yes

152,416 (5.40)

150,104 (5.38)

2,312 (6.60)

Premature birth, n (%)

No

2,569,761 (90.98)

2,539,204 (91.03)

30,557 (87.26)

Yes

254,657 (9.02)

250,194 (8.97)

4,463 (12.74)

NICU admission, n (%)

No

2,621,722 (92.82)

2,590,534 (92.87)

31,188 (89.06)

Yes

202,696 (7.18)

198,864 (7.13)

3,832 (10.94)