Troy Brown, RN
March 11, 2019
Infants born to women who smoked even one cigarette per day during pregnancy had more than twice the risk for sudden unexpected infant death (SUID) compared with those whose mothers did not smoke, and that risk increased with each cigarette, a large study found. The risk fell when women reduced or quit smoking.
"Compared with the pregnant smokers who did not reduce their smoking during pregnancy (more than half), those who reduced the number of cigarettes smoked by the third trimester demonstrated a modest (12%) decrease in the risk of SUID, and quitting by the third trimester was associated with a greater reduction in risk (by 23%)," the researchers write.
The study, by Tatiana M. Anderson, PhD, Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington, and colleagues, was published online March 11 in Pediatrics.
The researchers analyzed vital statistics data for 20,685,463 births and 19,127 SUIDs, adjusting for race and/or ethnicity/Hispanic origin of mother and father, mother's and father's age, mother's marital status, mother's education, live birth order, number of prenatal visits, gestational age in weeks, delivery method (vaginal or cesarean), infant sex, and birth weight.
SUID includes sudden infant death syndrome, accidental suffocation and strangulation in bed, and ill-defined causes.
Compared with nonsmokers, the risk for SUID was more than double among infants of mothers who reported any smoking during pregnancy (adjusted odds ratio [aOR], 2.44; 95% confidence interval [CI], 2.31 – 2.57).
The risk was almost twice as high with one cigarette smoked per day (aOR, 1.98; 95% CI, 1.73 – 2.28), and it increased linearly until plateauing at 3.17 (95% CI, 2.87 – 3.51) for those who smoked a pack (20 cigarettes) a day.
"This correlation was similar for each trimester when modelled independently, but the average number of cigarettes in the 3 trimesters together provided greater predictive power," the researchers explain.
The findings suggest "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 (20 cigarettes per day) smokers," the researchers write.
More than half (55%) of mothers who smoked during pregnancy continued to smoke as many cigarettes as they had before pregnancy. On average, those who quit smoking by the beginning of the third trimester (20%) cut the number of cigarettes smoked during pregnancy by 58%, and those who reduced their smoking by the third trimester cut the number of cigarettes by 33%. This was a "measurable reduction," the researchers say.
Compared with those who continued to smoke, SUID risk was slightly lower in the reduced-smoking group (aOR, 0.88; 95% CI, 0.79 – 0.98), although the largest reduction in risk was seen in the group who quit (aOR, 0.77; 95% CI, 0.67 – 0.87).
Compared with not smoking during pregnancy or the 3 months before, the risk for SUID increased progressively for mothers who smoked and quit before pregnancy (aOR, 1.47; 95% CI, 1.16 –1.87), those who did not smoke before pregnancy but smoked while they were pregnant (aOR, 2.22; 95% CI, 1.15 – 4.29), and those who smoked before and during pregnancy (aOR, 2.52; 95% CI, 2.25 – 2.83).
For those who only smoked before pregnancy, the amount of smoking did not appear to affect SUID risk.
The researchers believe the smoking estimates are likely conservative, because they did not evaluate prenatal or postpartum environmental smoke exposure, including paternal smoking, which is known to affect SUID risk. In addition, the smoking estimates rely on reports by the women, who may have been reluctant to disclose their smoking status.
Women should be "strongly encouraged" to not smoke during pregnancy and to reduce the amount they smoke, the authors say. "We estimate that US SUID rates could be reduced by 22% if no women smoked during pregnancy," they conclude.
The study was supported by the National Institutes of Health, Microsoft, and the Aaron Matthew Sudden Infant Death Syndrome Research Guild. The authors have disclosed no relevant financial relationships.