Prenatal exposure to cigarettes in infants with obstructive sleep apneas

To investigate the effect of prenatal smoking on infant respiratory behavior during sleep.

A questionnaire concerning family habits and infants' history was completed for 550 healthy infants before a 9-hour night polysomnographic study. Because the data for 41 infants were not available for analysis, 509 subjects were studied: 115 were newborns evaluated within 1 week after birth, and 394 were healthy infants admitted at 11 weeks of life (range 5 to 29 weeks) after various research protocols.

According to the smoking frequency of the mothers during pregnancy, the subjects were defined as "nonsmokers" (no cigarette smoked during pregnancy; n = 400), "light smokers" (1 to 9 cigarettes per day; n = 37), or "smokers" (10 or more cigarettes per day; n = 72). Compared with nonsmokers and light smokers, "smoking" mothers had a significant increase in the number of episodes of uterine bleeding during the pregnancy. Their infants had lower birth weights and more frequent episodes of profuse sweating during sleep. Infants of smokers also had more frequent and longer obstructive sleep apneas than those of the two other groups. For infants of smokers the relative risk for obstructive apneas was 2.76 (95% confidence interval: 1.63 to 4.69; P = .001). The relation between prenatal smoking and postnatal manifestation of obstructive sleep apneas demonstrated a dose-response pattern. Paternal smoking during pregnancy increased the risk of obstructive apneas only in the infants of smoking mothers, but not in those of the two other groups. Maternal smoking after birth did not add significantly to the risk of obstructive apneas. The effect of smoking was seen in older infants, as well as in the newborn not yet exposed to ambient cigarette smoke. A stepwise logistic regression, using obstructive sleep apneas as the dependent variable identified three significant independent variables: smoking during pregnancy (P = .001), profuse sweating during sleep (P = .001), and birth weight (P = .010). No explanation was found for the effect of prenatal smoking on obstructive sleep apneas.

Prenatal smoking by mothers correlated with an increase in frequency and length of obstructive apneas and a decrease in birth weight of their infants. The infants were under greater risk for obstructive apnea if both parents smoked. Explanations for our results are unknown to us, but these findings may be of interest in the study of infant breathing behavior and epidemiological characteristics of sudden infant death syndrome.