Sudden infant death (SID) is associated with both intrauterine growth retardation and maternal smoking during pregnancy. Here, we investigated if the statistical association between maternal smoking and SID is direct or mediated through the well-known growth retarding effects of heavy maternal smoking on the fetoplacental unit. We analysed data from a population-based prospective cohort study (181 cases, total newborn population 227,791 births) within the Westphalian Perinatal Inquiry in Germany between 1990 and 1994. SID victims whose mothers did not smoke had a normal mean birth weight (mean 3415.5 vs 3431.5 g), length (mean 51.46 vs 51.66 cm), and body mass index (BMI) (mean 12.8 vs 12.8 kg/m2) when compared to surviving children. In contrast, SID victims of mothers who smoked heavily (> ten cigarettes per day) had a significantly lower birth weight (2911.21 g vs 3148.34 g), length (48.98 vs 50.39 cm), and BMI (11.8 vs 12.4 kg/m2) when compared to surviving children whose mothers smoked heavily. Stratification for gestational age revealed that these differences are mainly caused by preterm SID infants.
Conclusion: The statistical association between maternal smoking and SID mainly results from effects of tobacco smoke on the fetoplacental unit which, in later SID victims, appears to be more susceptible to the growth retarding effects of cigarette smoking.