Smoking a factor in infant death disparities

NEW YORK (Reuters Health) - Poor women are more likely to smoke while pregnant and this helps explain some, but not all, of their greater risk of having a stillborn infant, new research shows.

The findings are "encouraging, in a way," because they suggest that helping women quit could help eliminate social and economic disparities in stillbirth and infant death, Dr. Ron Gray of the University of Oxford, the study's lead author, told Reuters Health.

Stillbirths and infant deaths are clearly linked to deprivation and poverty, Gray and his colleagues point out in the latest issue of the British Medical Journal, while the association between smoking in pregnancy and infant mortality is also well-established.

Since socioeconomic class is known to play a role in whether or not a woman smokes in pregnancy, the researchers sought to quantify the relationship by analyzing records on babies born in Scottish hospitals between 1994 and 2003. Their analysis included 529,317 babies born alive and 2,699 stillbirths at 24 to 44 weeks' gestation.

Thirty-eight percent of the women living in the most deprived neighborhoods admitted to smoking while they were pregnant compared to 13 percent of the women living in the least deprived neighborhoods.

They calculated level of deprivation by using the Carstairs-Morris index, which assigns a number from one to five to a given postal code by incorporating percentages of adult male unemployment, household overcrowding, car ownership, and households with a working member belonging to a lower social class.

Stillbirths were 56 percent more common among the most deprived women, and these women were 72 percent more likely to have babies who died in the first year of life, the researchers also found.

A "really striking" finding, they note, is that the likelihood of having a baby die after 28 days of age but before one year was two-and-a-half times more common among the most deprived mothers compared to the least deprived mothers.

Gray and his team determined that smoking in pregnancy was responsible for 38 percent of the difference in stillbirths and 31 percent of the difference in infant deaths.

Women in the study were only asked whether or not they smoked at a single time point, the researchers note. But babies exposed to smoke in the womb may be more likely to be exposed in the first year of life as well, they add, "an established risk factor" for death in infancy, especially sudden infant death syndrome (SIDS).

"Nicotine is a very addictive substance and it's very difficult to stop smoking at any time, especially during pregnancy," Gray said in an interview. "Clearly people need a lot of help to do this. There needs to be more investment in these kinds of services."

But this is not enough, he added. "I think there are other issues as well, such as tackling family and child poverty, improving access to health and maternity care for low income women, and ... things in general to improve deprivation such as neighborhood renewal schemes."

SOURCE: BMJ, online October 1, 2009.