Passive smoking is associated with earlier delivery and lower birth weight

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.

Paper

‘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