Exposure to passive smoking is associated with lower birth weight, infection and stillbirth, says new research published today in BJOG: An International Journal of Obstetrics and Gynaecology.

A Canadian study looked at 11,852 non-smoking women over an eight year period. Women who self reported exposure to passive smoking were compared to those who reported no exposure.

Undiluted side stream smoke contains many harmful chemicals and in greater concentration than cigarette smoke inhaled through a filter.

Of the 11,852, 1,202 (11.1%) were exposed to passive smoking and 10,650 (89.9%) self reported no exposure.

A number of adverse outcomes were seen more frequently in women exposed to passive smoking including smaller head circumference, lower birth rate, increased rates of stillbirths and preterm birth less than 37 and 34 weeks of gestation.

Women exposed to passive smoking were more than twice as likely to have a stillbirth according to the research. In the exposed group, 0.83% of women had a stillbirth compared to 0.37 of women in the non exposed group.

In the exposed group, 7.40% of women had babies with a birth weight of less than 2500 grams compared to 4.63% in the non exposed group.

In addition, women exposed to passive smoking were twice as likely to have babies with bacterial sepsis. In the exposed group, 1.08% had sepsis compared to 0.51% in the non exposed group.

Nonsmoking women exposed to passive smoking were found to be younger, had a higher BMI, were more likely to be nulliparous, less likely to have a partner, less likely to work, more likely to use alcohol or illicit drugs during pregnancy, and had a lower level of education than women not exposed to passive smoking.

The level of exposure to smoking was not reported in the study however as the exposure was based on self reporting.

Dr Crane, from the Department of Obstetrics and Gynaecology, Memorial University, St John's, Canada and lead author on the paper said:

"This information is important for women, their families and healthcare providers, and reinforces the continued need for increased public policy and education on prevention of exposure to second hand smoke during pregnancy."

BJOG Scientific Editor, Patrick Chien, said:

"Smoking while pregnant has been shown to have adverse effects on fetal development, however, this research also highlights the possible risks associated with second hand smoke.

"It is important that pregnant women lead a healthy lifestyle and are aware of the risks of passive smoking."

Reference

Crane J, Keough M, Murphy P, Burrage L, Hutchens D. Effects of environmental tobacco smoke on perinatal outcomes: a retrospective cohort study. BJOG 2011; DOI: 10.1111/j.1471-0528.2011.02941.x.

Source:
Royal College of Obstetricians and Gynaecologists