Odds of sudden unexpected infant death (SUID) more than doubled with maternal prenatal smoking and increased linearly with each additional cigarette mothers smoked during pregnancy, but quitting smoking during pregnancy cut SUID risk, according to a new study in.
“As prevalence of prone sleeping has declined, the relative contribution of prenatal maternal smoking to the risk of sudden infant death has increased,” Tatiana M. Anderson, PhD, of the Seattle Children’s Research Institute and her associates reported. When the researchers considered causality, they estimated that approximately 800 infants (22% of all SUID cases) per year in the United States could be attributed to maternal smoking during pregnancy.
The researchers analyzed 19,127 SUID cases among 20,685,463 births included in the Centers for Disease Control and Prevention Birth Cohort Linked Birth/Infant Death Data Set for 2007-2011. A SUID diagnosis included sudden infant death syndrome, infant death from ill-defined or unknown cause, and accidental suffocation or strangulation in bed for any infants under 1 year old.
When the authors calculated odds related to prenatal maternal smoking and SUID, they adjusted for infant sex and birth weight, gestational length of pregnancy, delivery method (vaginal or cesarean), total prenatal visits, live birth order, maternal marital status and education, and maternal and paternal age and race/ethnicity.
Any maternal smoking at all during pregnancy was associated with more than twice the odds of SUID (adjusted odds ratio, 2.44). Odds of SUID also doubled for smoking one cigarette daily during pregnancy versus smoking none. For each additional cigarette smoked daily during pregnancy, odds of SUID increased by 0.07 up until 20 cigarettes, when the risk evened out, which suggests “that smoking cessation efforts may have greater impact on decreasing SUID rates when directed toward those who smoke fewer than 1 pack per day versus the more traditionally targeted heavy ([more than] 20 cigarettes per day) smokers,” the authors wrote.
Odds of SUID dropped 12% when mothers cut down on smoking during pregnancy and dropped 23% when they quit altogether (aORs, 0.88 and 0.77, respectively). “However, there may be some selection bias because the group who reduced smoking started at a higher average number of cigarettes in the first trimester, whereas those who successfully quit smoked fewer cigarettes in the first trimester,” the authors noted.
Among the 11.6% of mothers who said in 2011 that they smoked in the 3 months leading up to pregnancy, only a quarter quit while pregnant, the authors wrote. Quitting after having smoked before pregnancy was linked to a 47% increased risk of SUID, although the researchers noted that second- and third-hand smoke may have played a role since mothers who smoke may begin smoking again post partum and/or often have a partner who smokes.
“This group may have also included women who stopped smoking as soon as they knew they were pregnant and thus reported that they were nonsmokers in the first trimester, but the fetus had been exposed to maternal smoking during the period before pregnancy was diagnosed,” the authors wrote. They also acknowledged the possibility of residual confounding, particularly from socioeconomic factors or alcohol consumption during pregnancy.
The research was funded by the National Institutes of Health, Microsoft, and the Aaron Matthew Sudden Infant Death Syndrome Research Guild. One author has testified as a paid expert in a SUID case. No other authors reported conflicts of interest.
SOURCE: Anderson TM et al. Pediatrics. 2019 March 11.