Despite awareness of negative health outcomes associated with smoking, pregnant smokers might reduce their tobacco consumption thinking that a low smoking rate reduces smoking-related negative birth outcomes. We aimed to assess in a clinical sample whether there is a smoking rate that would not impact on birth weight (BW).
Pregnant smokers ≥18 years, gestational age of 9-20 weeks of amenorrhea, motivated to quit smoking, smoking ≥5 cigarettes/day (cpd) and their newborns (381 singleton, live births) were included in this secondary analysis of a French smoking cessation trial.
The mean BW when the mother quit smoking was 3417 g (95 % CI: 3098-3738 g); when smoking >0<5 cpd, 3081g (3003-3159 g); when smoking 5-9 cpd, 3043 g (2930-3157 g); and when smoking ≥10 cpd, 2831 g (2596-3157 g) (p = .006). The corresponding effect sizes ranged from medium to large (Cohen's d for BW: 0.54, 0.57 and 0.85) compared to BW when the mother quit. In the multivariable analysis, adjusted for all significant confounders, when the mother smoked on average >0<5 cpd, the loss in BW was 228 g; when smoking 5-9 cpd, 251 g; and when smoking ≥10 cpd, 262 g (all p ≤ .02) compared to newborns' BW of mothers who stopped smoking since quit date.
Even low cigarette consumption during pregnancy is associated with BW loss. All efforts should be made to help pregnant smokers quit completely during their pregnancy.
As an alternative to quitting smoking, pregnant smokers reduce their smoking rate thinking that this diminishes smoking-related negative health outcomes. No study has established whether low smoking rate (more than 0 but less than 5 cpd) during pregnancy impacts BW compared to abstinence from smoking. Among treatment-seeking pregnant smokers BW of newborns of mothers who smoked even less than 5 cpd was significantly lower than of those whose mothers quit; effect sizes of different consumption levels on BW ranged from moderate (>0<5 cpd) to large (≥10 cpd). Even low smoking rate is associated with reduced BW compared to complete maternal smoking abstinence.