Smoking in pregnancy as a risk factor for long-term mortality in the offspring

This study addresses the question of whether maternal smoking is related to postneonatal mortality and which are the contributing causes of death. Mortality of births in Sweden between 1 January 1983 and 31 December 1989 (n = 714,389) registered in the Medical Birth Registry was followed until 31 December 1990. The registry carries information on maternal smoking habits in early pregnancy. The Mantel-Haenszel procedure was used to control for confounding effects of maternal age, parity and year of birth: relative risks (95% confidence interval) associated with smoking were: 1.24 (1.17-1.31) for fetal death, 1.08 (1.01-1.16) for early neonatal death, 1.22 (1.08-1.39) for late neonatal death, 1.31 (1.23-1.41) for postneonatal mortality during the first year, and for the period between 1 and 8 years of age it was 1.19 (1.06-1.32). When birthweight was controlled for, the increased relative risk for postneonatal mortality during the first year disappeared. Mortality between 1 and 8 years still showed an elevated risk of 1.43 (1.00-2.06). In order to control for confounding by social factors, 1986 births were linked to data from the 1985 Swedish census. The measure used was the socio-economic index (SEI), which reflects the parental education level. When maternal, paternal or family SEI was controlled for, late neonatal death was not significantly related to maternal smoking, but postneonatal death still showed a significantly increased relative risk of about 1.35. Four causes of death based on International Classification of Diseases (ICD) 8 and 9 were significantly related to maternal smoking: sudden infant death syndrome, injuries and poisoning, perinatal causes and infections.