Scientists at Roswell Park Cancer Institute (RPCI) and the University at Buffalo (UB) in the US found that women with the highest levels of secondhand smoke exposure had significantly greater estimates of risk for all three adverse pregnancy outcomes.
"This study demonstrated that pregnancy outcomes can be correlated with secondhand smoking. Significantly, women who have never smoked but were exposed to secondhand smoke were at greater risk for foetal loss," said the study's lead investigator, Andrew Hyland, Chair of RPCI's Department of Health Behaviour.
The study is significant in two ways: Firstly, it considered lifetime secondhand smoke (SHS) exposure rather than only during pregnancy or reproductive years, taking into consideration smoke exposure in participants' childhood and adult years, researchers said.
Secondly, the comparison group of never-smokers was limited to women without any SHS exposure, producing a truer control group compared to previous studies.
Historical reproductive data, current and former smoking status, and details about SHS exposure over lifetime were collected from the Women's Health Initiative Observational Study. This allowed for a study group of 80,762 women.
Women with the highest levels of SHS 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 smoke (those who smoked more than 100 cigarettes in their lifetime).
The highest levels of lifetime SHS exposure were defined by childhood exposure for longer than 10 years, adult home exposure for more than 20 years and adult work exposure for more than 10 years.
"This study offers new information for women regarding the lifetime impact secondhand smoke can have on reproductive outcomes and their ability to successfully bring a pregnancy to full term," said Hyland.
The study was published in the journal Tobacco Control.