INTERACTIONS BETWEEN MATERNAL SMOKING AND OTHER PRENATAL RISK-FACTORSFOR SUDDEN-INFANT-DEATH-SYNDROME (SIDS)

In numerous investigations, maternal smoking increases the risk of sud den infant death syndrome (SIDS). In the present study we investigated whether prenatal risk factors for SIDS modify the effect of maternal smoking on SIDS mortality. We analysed data from a population-based co hort study (222 cases, 260,604 infants at risk) within the Westphalian Perinatal Inquiry in Germany between 1990 and 1994. In the stratified analysis, smoking was classified into non-smoking, moderate (1-10 cig arettes/d) and heavy smoking (> 10 cigarettes/d). Multiplicative inter actions between smoking and other prenatal risk factors were assessed in a logistic regression model. The relative risk (RR) for maternal sm oking was 2.4 (95% confidence interval 1.7-5.4) for moderate and 7.2 ( 5.3, 9.7) for heavy smokers. Previous established risk factors for SID S, such as preterm birth, low birthweight, and number of prenatal visi ts did not increase the risk of SIDS among non-smokers, but became imp ortant risk factors among smokers. In preterm infants (< 37 weeks) of heavy smokers, the RR was 19.6 (10.4, 36.8) compared to term infants o f non-smokers. Low birthweight infants (< 2500 g) of heavy smokers had a RR of 16.3 (8.4, 31.2) compared to normal weighted infants of nonsm okers. Adjustment for occupational status did not change the crude est imates. The RR of < 6 prenatal visits in the heavy smoking subgroup wa s 14.8 (7.2, 29.6) compared to > 9 prenatal visits in the non smoking strata. Heavy smoking potentiates other prenatal risk factors for SIDS suggesting an increased susceptibility towards the adverse effects of tobacco smoke in utero. In infants born to non-smoking mothers, prena tal risk factors are absent and postnatal factors may be of major impo rtance.