Table 2

 Percentage change in risk of preterm delivery in association with the successive implementation of public smoking bans. Values are percentage change (95% CI)

ModelLegislation 2006Legislation 2007Legislation 2010
Step change‡Slope change§Step change‡Slope change§Step change‡Slope change§
Spontaneous preterm delivery
2006†−3.24 (−4.40 to −2.07)*−1.85 (−2.42 to −1.28)*N/AN/AN/AN/A
2007†N/AN/A−3.69 (−4.81 to −2.55)*−2.16 (−2.85 to −1.46)*N/An/a
2010†N/AN/AN/AN/A−3.36 (−4.73 to −1.98)*−5.17 (−7.36 to −2.94)*
Final−3.13 (−4.37 to −1.87)*−2.65 (−5.11 to −0.13)*
Overall preterm delivery
2006†−0.59 (−2.63 to 1.49)−1.95 (−3.50 to −0.37)*N/AN/AN/AN/A
2007†N/AN/A−2.28 (−4.37 to −0.15)*−1.42 (−2.87 to 0.05)**N/AN/A
2010†N/AN/AN/AN/A−1.24 (−3.05 to 0.60)−2.10 (−4.82 to 0.69)
Final——−3.18 (−5.38 to −0.94)*−3.50 (−6.35 to −0.57)*

Percentage change based on odds ratios derived from logistic regression models and adjusted for underlying trend, newborn sex, maternal age, parity, socioeconomic status, urbanisation, calendar month, day of the week, public holidays, influenza epidemics, and short term changes in apparent temperature and particulate air pollution (PM10). Final models were obtained by including the three step changes and the three slope changes in one model and then removing the least significant factors one at a time.

*P<0.05; **P<0.1.

†Single-legislation models including either the step change or the slope change into the model.

‡Step change at 1 January 2006 (legislation 2006), 1 January 2007 (legislation 2007), or 1 January 2010 (legislation 2010).

§Slope change after 1 January 2006 (legislation 2006), 1 January 2007 (legislation 2007), or 1 January 2010 (legislation 2010).

N/A = Not applicable.