Table 2 Associations between sociodemographic, health and lifestyle factors and the odds of preterm birth

Group assignment

1.20 (0.82 – 1.76)

1.14 (0.78 – 1.68)

1.15 (0.78 – 1.69)

1.18 (0.80 – 1.73)

BMI category^a

  BMI 25.0 – 29.9 kg/m²

1.39 (0.89 – 2.15)

1.43 (0.92 – 2.22)

1.41 (0.90 – 2.20)

1.37 (0.88 – 2.14)

  BMI 30.0 – 40.0 kg/m²

1.14 (0.63 – 2.08)

1.10 (0.60 – 2.02)

1.09 (0.59 – 1.99)

1.04 (0.56 – 1.91)

Age^b

  26 – 35 years

1.52 (0.78 – 2.98)

1.69 (0.86 – 3.32)

1.70 (0.86 – 3.36)

1.82 (0.92 – 3.63)

  36 – 43 years

2.06 (0.94 – 4.55)

2.52 (1.12 – 5.65)⁺

2.53 (1.13 – 5.67)⁺

2.70 (1.20 – 6.10)⁺

Nulliparity

1.63 (1.08 – 2.45)⁺

1.64 (1.08 – 2.47)⁺

1.58 (1.02 – 2.42)⁺

Early GWG^c

  Excessive

0.99 (0.53 – 1.84)

1.00 (0.54 – 1.86)

0.98 (0.53 – 1.83)

  Inadequate

1.23 (0.63 – 2.41)

1.25 (0.64 – 2.44)

1.18 (0.60 – 2.32)

Smoking^d

0.70 (0.25 – 1.97)

0.64 (0.23 – 1.81)

Low education^e

1.25 (0.73 – 2.14)

1.18 (0.68 – 2.03)

Low HEI^f

1.54 (1.04 – 2.30)⁺

Low PA^g

1.04 (0.69 – 1.55)

Antenatal anxiety/

distress^h

1.01 (0.69 – 1.50)