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Passive smoking is associated with earlier delivery and lower birth weight

24 November 2015

It has been known for more than 50 years that a mother who smokes whilst pregnant is more likely to give birth to her baby prematurely. But what if a mother doesn’t smoke but lives with someone who does? New research by academics from the University of Bristol has found women exposed to passive smoking, on average, deliver their babies earlier and with lower birth weights compared to unexposed women.

The study, published online in Reproductive Sciences, included more than 5,000 women delivering their babies in Bristol between 2012 and 2014. The researchers used both a woman’s report of her exposure to passive smoking as well as an objective measurement – an exhaled carbon monoxide reading in early pregnancy. Many other factors were considered too, including maternal age, weight, ethnicity, as well as employment and social circumstances.

The research team found that non-smoking women that lived with someone who smoked were more likely to deliver their babies earlier compared to women not living with a smoker. They also found these women exposed to passive smoking had smaller babies. Although the effect on gestational age at delivery was around a third smaller than when a woman herself smoked, more women are affected by passive smoking. About one in seven women smoke through their pregnancies but more than one in four non-smoking women live with a smoker and are exposed to these increased risks from passive smoking.

Dr Rachel Ion from Bristol’s School of Clinical Sciences and St Michael’s Hospital, who led the research, said: “Women are generally aware of the risks of smoking during pregnancy but more education is needed to inform women and their families and friends of the emerging evidence of the risks associated with passive smoking in pregnancy. Our results add evidence to public health arguments to implement further measures to reduce exposure to passive smoking.”

Babies that are born too early can suffer from many complications. Premature birth accounts for more than a million deaths each year worldwide. Those babies that survive can face significant long-term problems including breathing difficulties and cerebral palsy. Premature birth affects not only the child, but their family and society as a whole with significant healthcare costs associated with caring for these children. Although the study did not look at these long-term outcomes the finding that passive smoking is associated with earlier delivery highlights the importance of studying environmental factors such as this.


Environmental tobacco smoke exposure in pregnancy is associated with earlier delivery andreduced birth weight’ by Rachel C. Ion, Andrew K. Wilis and Andres Lopez Bernal in Reproductive Sciences

Passive smoking is associated with earlier delivery and lower birth weight
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