Perinatal events associated with maternal smoking during pregnancy

To identify components of smoking-related increased perinatal mortality, detailed analyses of data from the Ontario Perinatal Mortality Study (50,000 births, 1,300 deaths, 1960-1961) measured the relationship of maternal smoking .to birth weight, gestation, placental complications, and perinatal mortality. Cross-tabulations with other factors and multiple adjustment showed increases with amount smoked of birth weights <2500 gm, gestations <38 weeks, placenta previa, abruptio placentae, and perinatal mortality. These significant, smoking-related increases were independent of mother's height, weight, hospital status, age-parity group, birthplace, previous pregnancy history, weight gain, time of registration, and sex of child.Maternal smoking had the strongest effect on birthweight in the 8 factor regression, and births <2500 gm increased directly with smoking level from 20% to 340% in 37 data subgroups. Births <38 weeks increased 20% and 50% and perinatal mortality increased 20% and 36% for <1 pack and 1 + pack smokers, respectively, adjusted for 7 other factors. Placental complications increased consistently with smoking level in all of 37 subgroups except for primiparous < 1 pack smokers. Adjusted rates increased 25% and 92% for placenta previa, 23% and 86% for abruptions among smokers of < 1 pack and 1 + packs, respectively. These complications carry high perinatal mortality risk, and account for one-third to one-half of the perinatal deaths attributable to maternal smoking.