NEW YORK (Reuters Health) - A large study that followed women through their first and second consecutive pregnancy provides additional evidence of a direct link between smoking and increased risk of stillbirth.
Compared with women who didn't smoking during either pregnancy, the investigators found that those who smoked during their first but not their second pregnancy did not have an increased risk of stillbirth. However, women who smoked during both consecutive pregnancies had a 35 percent higher risk of stillbirth than nonsmokers.
Because the study found a reduction in stillbirth risk among women who quit smoking, it suggests that smoking can cause infants to not survive delivery, Drs. L. Hogberg and S. Cnattingius of the Karolinska Institutet in Stockholm, Sweden conclude.
There is a well-established association between smoking during pregnancy and stillbirth, but evidence supporting a causal link has been mixed, Hogberg and Cnattingius note in BJOG: An International Journal of Obstetrics and Gynecology.
To investigate how changes in smoking habits might affect stillbirth risk, the researchers looked at data from a nationwide birth registry of 526,691 women who had delivered their first and second children between 1983 and 2001.
Women who smoked during their first pregnancy but quit during their second pregnancy were no more likely to have a stillborn infant than those who never smoked at all.
As mentioned, overall, women who smoked during both their first and second pregnancies were at a 35 percent greater risk of delivering their second child stillborn. In addition, heavy smokers, defined as 10 or more cigarettes per day, had a 45-percent increased risk of having a stillborn infant in their second pregnancy, while smoking one to nine cigarettes per day during the second pregnancy did not increase stillbirth risk.
While 31 percent of the women smoked every day in early pregnancy in 1983, that number fell to 10 percent by 2003, the researchers note. Nevertheless, they conclude, "As smoking is a preventable risk factor for stillbirth and other adverse pregnancy outcomes, smoking interventions should continue to have a high priority in the work of antenatal care centers."
SOURCE: BJOG: An International Journal of Obstetrics and Gynecology, June 2007.
