"This study demonstrated pregnancy outcomes could be correlated with secondhand smoking," lead investigator Andrew Hyland of Roswell Park Cancer Institute in Buffalo, N.Y., said in a statement.
"Significantly, women who never smoked but were exposed to secondhand smoke were at greater risk for fetal loss."
Previous research showed smoking during pregnancy was associated with the three outcomes of fetal loss studied -- spontaneous abortion or miscarriage, or loss of a fetus before 20 weeks of gestation; stillbirth, or loss of a fetus after 20 or more weeks of gestation, and tubal ectopic pregnancy.
This study is significant in two ways: One, it considered lifetime secondhand smoke exposure rather than only during pregnancy or reproductive years, taking into consideration smoke exposure in participants' childhood and adult years. Two, the comparison group of never-smokers was limited to women without any secondhand smoke exposure, producing a truer control group compared to previous studies, Hyland said.
Researchers at Roswell Park and the University at Buffalo used historical reproductive data, current and former smoking status and details about secondhand smoke exposure over a lifetime from more than 80,000 women from the Women's Health Initiative Observational Study.
The study, published in the journal Tobacco Control, found women with the highest levels of secondhand smoke exposure -- despite never having smoked themselves -- had significantly greater estimates of risk for all three adverse pregnancy outcomes. These risks approached the risk seen among women who smoked more than 100 cigarettes in their lifetime, the study said.
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