Table 1 Baseline characteristics of participations

Age ^a

32.00 (28.00,35.00)

32.00 (29.00,35.00)

−2.889

0.004

Gestational age (weeks)^a

39.57 (38.71,40.29)

39.57 (38.71,40.29)

0.614

0.539

Gravidity^a

2.00 (2.00,4.00)

2.00 (1.00,3.00)

15.750

< 0.001

Parity^a

1.00 (0.00,2.00)

1.00 (0.00,1.00)

25.976

< 0.001

Maternal height (cm) ^a

162.60 (157.50,167.60)

163.00 (160.00,168.00)

−5.915

< 0.001

Maternal BMI (kg/(m)²)^a

28.95 (26.08,32.53)

29.21 (26.42,32.89)

−3.422

0.001

Baby height (cm) ^a

50.00 (48.30,52.00)

50.50 (48.30,52.10)

−5.013

< 0.001

Baby weight (kg) ^a

3.35 (3.04,3.65)

3.35 (3.04,3.66)

−0.160

0.873

Preterm delivery^b

287 (5.7%)

1261 (5.6%)

0.128

0.721

Multiple pregnancy^b

29 (0.6%)

490 (2.2%)

56.513

< 0.001

Induction^b

810 (16.1%)

7536 (33.0%)

579.495

< 0.001

Oxytocin^b

949 (18.9%)

12,513 (55.3%)

2191.814

< 0.001

Operative delivery^b

95 (1.9%)

1744 (7.7%)

224.805

< 0.001

Ethnic^b

195.759

< 0.001

 White

2820 (56.1%)

14,968 (66.2%)

 Black

597 (11.9%)

1818 (8.0%)

 others

1613 (32.1%)

5822 (25.8%)