Smoking during pregnancy heightens sudden infant death chances

Washington, Aug 30 : Women who smoke during pregnancy have greater chances of losing their newborns to the sudden infant death syndrome (SIDS), according to new research carried out by Calgary University.

In the first-ever experimental study to compare the breathing reflexes of premature babies of smokers versus non-smokers, researchers found that babies whose mothers had smoked showed a number of signs of impaired respiratory function.

"Smoking during pregnancy is a double-edged sword with respect to SIDS," said Shabih Hasan, professor in the department of paediatrics at the University of Calgary, and the principal investigator of the study.

"Not only does it raise a mother's likelihood of having a preterm baby, who is already among the most vulnerable to SIDS, but it increases the infant's susceptibility to SIDS even further."

The study results are scheduled for publication in the September issue of the American Thoracic Society's Journal of Respiratory and Critical Care Medicine.

Earlier studies have indicated that a combination of hypoxia (low oxygen) and hypercarbia (excess of carbon dioxide) may be acute precursors to SIDS. Infants at the greatest risk for SIDS have been shown to have both attenuated arousal and ventilatory responses to hypoxia and /or hypercarbia.

"Preterm (premature) babies are known to have increased breathing difficulties in proportion to their prematurity and cigarette smoke is known to increase apneas in full-term babies," said Hasan.

"But until now, cigarette smoke exposure and preterm birth have not been investigated together with respect to their potential effects on respiratory dysfunction."

To analyse the effects of cigarette smoke exposure on preterm infants' respiratory health and their risk of SIDS, researchers recruited 22 preterm infants who had been spontaneously born between 28 and 32 weeks with no other complicating respiratory factors.

Twelve of the infants had mothers who had smoked five or more cigarettes every day during pregnancy. The mothers of the other ten infants did not smoke during pregnancy.

The researchers obtained baseline readings on the infants' breathing patterns in normal conditions, assessing breathing rate, pauses in breathing, recovery period and heart rate.

Saturation of oxygen in their blood was also monitored. After baseline readings were recorded, the infants were challenged with a five-minute period of decreased oxygen delivered through a nasal cannula. During this period they were monitored very closely with infant resuscitation equipment near at hand.

The two groups were remarkably similar in some measures: respiratory rates and number of breathing pauses were similar among both groups of infants.