The study reveals that more than 40% of all pregnant women in Pakistan are exposed to secondhand smoke—causing approximately 17,000 still births in a year.
Exposure to secondhand smoke during pregnancy increases the risk of stillbirth, congenital malformations, low birth-weight and respiratory illnesses. However, little is known about the extent of secondhand smoke exposure during pregnancy.
The team from York looked at the number of pregnancies alongside smoking exposure data in 30 developing countries from 2008 to 2013.
The analysis revealed that in Armenia, Indonesia, Jordan, Bangladesh and Nepal more than 50% of pregnant women reported exposure to household secondhand smoke. The authors believe this led to over 10,000 still births in Indonesia alone.
In Pakistan only 1% of still births are attributed to women actively smoking during pregnancy, but for secondhand smoke the figure is 7%, largely due to the high numbers of pregnant women exposed to tobacco smoke in the home.
In five of the 30 countries, household secondhand smoke exposure was twice as common as active smoking.
Lead author, Professor Kamran Siddiqi, from the University of York's Department of Health Sciences, said it was predominately male smokers exposing women to secondhand smoke.
He said: "This is the first study which provides national estimates for 30 developing countries on secondhand smoke exposure in pregnancy and it reveals a huge problem, a problem which is not being addressed.
"We have shown for the first time that secondhand smoke during pregnancy is far more common than active smoking in developing countries, accounting for more still births than active smoking.
"Protecting pregnant women from secondhand smoke exposure should be a key strategy to improve maternal and child health."
The research team say the results are based on self-reported surveys and could be subject to underestimation.
They also say further work is needed to develop effective interventions to reduce household exposure to secondhand smoke.
The findings are published in the journal BMJ Tobacco Control and was partially funded by the Medical Research Council.
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Sian Reece et al, Secondhand smoke exposure during pregnancy: a cross-sectional analysis of data from Demographic and Health Survey from 30 low-income and middle-income countries, Tobacco Control (2018). DOI: 10.1136/tobaccocontrol-2018-054288