Medical science has firmly documented how smoking cigarettes during pregnancy contributes to increased risk of miscarriage and other disastrous complications of pregnancy. What is less well-documented is how — or if — passive (secondhand) smoke exposure produces the same negative effects. A recent study compared the effects of smoke exposure at various levels to the pregnancy outcomes of more than 80,000 women and discovered a clear link between secondhand smoke exposure and increased likelihood for miscarriage, stillbirths, and ectopic pregnancies. The more invasive the exposure to secondhand smoke over the woman’s lifetime, the greater her risk for complications.
In 1991, the US National Institutes of Health (NIH) launched the Women’s Health Initiative (WHI) to study prevention of diseases affecting post-menopausal American women. More than 160,000 women aged 50 to 79 enrolled in the multi-phased, long-term study. The racial composition of the study group mirrored that of the general American population. The WHI was the largest prevention-based study ever conducted in the US and the findings of the study are still being used today.
To explore the link between passive smoking and pregnancy risks, a research team led by Andrew Hyland of the Roswell Park Cancer Institute in Buffalo, New York, analyzed reproductive data involving 80,762 women in the WHI who had been pregnant at least once in their lifetimes. Their tobacco smoke exposure was categorized as:
- Current smokers — 6.3% of the study group — approximately 5,000 women
- Ex-smokers — 43% — slightly fewer than 35,000 women
- Non-smokers — 50.6% — approximately 41,000 women
Non-smokers were further categorized according to secondhand smoke exposure during childhood, at home as an adult, and on the job.
Pregnancy Risks for Smokers
Women who actively smoked at any time during their reproductive years were:
- 16% more likely to suffer miscarriage
- 44% more likely to have a stillborn
- 43% more likely to have an ectopic pregnancy
Pregnancy Risks for Non-Smokers in General
When exposed to the smoke of others during their lifetimes were:
- 32.6% miscarried at least one time
- 4.4% delivered a stillborn
- 2.5% had tubal (ectopic) pregnancies
Pregnancy Risk for Non-Smokers Exposed to Long-Term Passive Smoke
Women exposed to the smoke of others for 10 years or more during childhood, 20 years or more at home as an adult, or more than 10 years on the job were:
- 17% more likely to miscarry
- 55% more likely to deliver a stillborn child
- 61% more likely to experience an ectopic pregnancy
Regardless of smoke exposure, women of black and other ethnic minority backgrounds were more likely to miscarry or experience stillbirth or ectopic pregnancy. Younger women and those better educated were less like to experience any of the complications of birth cited in the study.
Source: Hyland, Andrew, et al. “Associations of lifetime active and passive smoking with spontaneous abortion, stillbirth and tubal ectopic pregnancy: a cross-sectional analysis of historical data from the Women’s Health Initiative.” Tobacco Control. The BMJ Publishing Group Ltd. Feb 26, 2014. Web. Mar 10, 2014.