Table 2 Maternal pre-pregnancy BMI and risks of preterm birth by gestational age

Parameters

Event/N (%)

Event/N (%)

OR (95% CI)

P

OR (95% CI)

P

Pre-pregnancy BMI group

< 0.001

0.072

 Normal weight (18.5–24.9)

1993/31599 (6.31%)

ref.

–

80/29686 (0.27%)

ref.

–

 Underweight (< 18.5)

431/6910 (6.24%)

1.06 (0.94 to 1.19)

0.339

13/6492 (0.20%)

0.70 (0.37 to 1.33)

0.281

 Overweight (25.0–29.9)

299/3295 (9.07%)

1.42 (1.23 to 1.63)

< 0.001

11/3007 (0.37%)

1.42 (0.75 to 2.69)

0.28

Obesity (≥30.0)

45/392 (11.48%)

2.01 (1.44 to 2.82)

< 0.001

3/350 (0.86%)

3.43 (1.07 to 10.97)

0.038

Event/N (%)

Event/N (%)

OR (95% CI)

P

OR (95% CI)

P

Pre-pregnancy BMI group

0.156

< 0.001

 Normal weight (18.5–24.9)

242/29848 (0.81%)

ref.

–

1671/31277 (5.34%)

ref.

–

Underweight (< 18.5)

47/6526 (0.72%)

0.96 (0.67 to 1.36)

0.8

371/6850 (5.42%)

1.09 (0.96 to 1.24)

0.171

 Overweight (25.0–29.9)

27/3023 (0.89%)

1.12 (0.73 to 1.72)

0.594

261/3257 (8.01%)

1.46 (1.26 to 1.69)

< 0.001

 Obesity (≥30.0)

6/353 (1.70%)

2.52 (1.11 to 5.74)

0.027

36/383 (9.40%)

1.87 (1.29 to 2.73)

0.001