Table 3 The odds of all preterm births (20- < 37 weeks gestation) and third trimester preterm births (28- < 37 weeks gestation) across maternal smoking status categories

Smoking Status

Crude OR

95% CI

Adjusted OR^a

95% CI

 No trimester smokers

0.85

0.82, 0.89*

0.90

0.86, 0.94*

 1st trimester only, low (ref.)

1

1

1

1

 1st trimester only, high

0.97

0.87, 1.08

0.98

0.88, 1.09

 1st & 2nd trimesters, low

1.53

1.43, 1.64*

1.51

1.41, 1.61*

 1st & 2nd trimesters, high

1.86

1.67, 2.07*

1.85

1.66, 2.06*

 2nd & 3rd trimesters, low

0.98

0.89, 1.08

0.95

0.86, 1.05

 2nd & 3rd trimesters, high

1.06

0.80, 1.41

1.03

0.77, 1.36

 All 3 trimesters, low

1.21

1.16, 1.26*

1.20

1.14, 1.25*

 All 3 trimesters, high

1.31

1.25, 1.38*

1.33

1.26, 1.40*

Smoking Status

Crude OR

95% CI

Adjusted OR^a

95% CI

 No trimester smokers

0.88

0.84, 0.92*

0.93

0.89, 0.97*

 1st trimester only, low (ref.)

1

1

1

1

 1st trimester only, high

0.96

0.86, 1.08

0.97

0.86, 1.08

 1st & 2nd trimesters, low

1.34

1.24, 1.44*

1.32

1.22, 1.42*

 1st & 2nd trimesters, high

1.62

1.44, 1.83*

1.61

1.43, 1.82*

 2nd & 3rd trimesters, low

1.03

0.93, 1.14

1.00

0.90, 1.11

 2nd & 3rd trimesters, high

1.09

0.81, 1.46

1.05

0.79, 1.40

 All 3 trimesters, low

1.27

1.21, 1.33*

1.25

1.20, 1.31*

 All 3 trimesters, high

1.39

1.32, 1.47*

1.40

1.33, 1.48*