Table 3 Maternal pre-pregnancy BMI and risks of clinical phenotypes of preterm birth

Parameters

Event/N (%)

Event/N (%)

OR (95% CI)

P

OR (95% CI)

P

Pre-pregnancy BMI group

0.021

< 0.001

 Normal weight (18.5–24.9)

694/30300 (2.29%)

ref.

–

496/30102 (1.65%)

ref.

–

 Underweight (< 18.5)

173/6652 (2.60%)

1.19 (0.99 to 1.43)

0.072

110/6589 (1.67%)

1.17 (0.94 to 1.47)

0.159

 Overweight (25.0–29.9)

82/3078 (2.66%)

1.21 (0.94 to 1.55)

0.138

82/3078 (2.66%)

1.62 (1.26 to 2.09)

< 0.001

Obesity (≥30.0)

14/361 (3.88%)

1.98 (1.13 to 3.47)

0.017

12/359 (3.34%)

2.04 (1.08 to 3.86)

0.029

Event/N (%)

OR (95% CI)

P

Pre-pregnancy BMI group

< 0.001

 Normal weight (18.5–24.9)

803/30409 (2.64%)

ref.

–

 Underweight (< 18.5)

148/6627 (2.23%)

0.87 (0.72 to 1.07)

0.182

 Overweight (25.0–29.9)

135/3131 (4.31%)

1.46 (1.19 to 1.80)

< 0.001

 Obesity (≥30.0)

19/366 (5.19%)

2.05 (1.25 to 3.37)

0.005