Secondhand Smoke Linked to Miscarriages, Stillbirths

Steven Fox

February 28, 2014

Secondhand smoke (SHS) exposure is linked to increased risks for miscarriage, stillbirth, and tubal ectopic pregnancy, according to results from a large observational study published online February 26 in Tobacco Control. The magnitude of the risk appeared to increase with increased exposure.

"These data and results in this study provide new evidence that suggest that SHS can have previously unstudied effects on pregnancy outcomes, " write Andrew Hyland, PhD, from the Department of Health Behavior, Division of Cancer Prevention and Population Sciences, Roswell Park Cancer Institute, Buffalo, New York, and colleagues.

Until now, evidence linking SHS to adverse pregnancy outcomes has only been suggestive. Therefore, the researchers assessed data on 80,762 postmenopausal women who had participated in the Women's Health Initiative Study, a nationwide observational study that gleaned data on a wide range of health topics.

About half (50.6%) of the women were never-smokers, 6.3% were currently smokers, and 43.1% had previously smoked.

The researchers categorized the never-smokers into several groups, based on level of exposure to SHS during childhood, as adults in the home, and as adults at work. Of the entire cohort, 32.6% (26,307) had experienced a miscarriage, 4.4% (3552) had experienced a stillbirth, and 2.5% (2033) had experienced at least 1 tubal ectopic pregnancy..

Risks of SHS exposure appeared to be cumulative, with risk accumulating with duration of exposure, the researchers report. Compared with nonsmoking women who had no SHS exposure, those who had experienced the highest levels of SHS exposure (defined as more than 10 years as a child, more than 20 years as an adult at home, or more than 10 years in the workplace) were 17% more likely to have miscarriages (odds ratio [OR] 1.17; 95% confidence interval [CI], 1.05 - 1.30), 55% more likely to deliver a stillborn child (OR, 1.55; 95% CI, 1.21 - 1.97), and 61% more likely to experience ectopic pregnancies (OR, 1.61; 95% CI, 1.27 - 2.04), the researchers write.

The figures for ex-smokers were also sobering. Compared with women who had never smoked, those who had smoked during their reproductive years were 16% more likely have experienced miscarriages (OR, 1.16; 95% CI, 1.08 - 1.26), 44% more likely to have experienced a stillbirth (OR, 1.44; 95% CI, 1.20 - 1.73), and 43% more likely to have experienced an ectopic pregnancy (OR, 1.43; 95% CI, 1.10 - 1.86).

Previous studies have shown varied results regarding the possible link between pregnancy risks and exposure to SHS. However, these investigators say the variability may be largely a result of methodology and that earlier studies did not include sufficient assessment of all lifetime periods of SHS exposure.

"Additionally, the reference group for many of these studies was not strictly limited to never-smokers not exposed to any SHS throughout life," the investigators write. In their view, this would have been a shortcoming that would dilute the power of previous studies.

The researchers note that data in the current study were gathered from 40 centers throughout the United States and included women from a wide range of ethnic, socioeconomic, and educational backgrounds, lending credence to the findings.

"This information significantly expands the scope of populations that are potentially impacted by SHS," the researchers conclude. "Continuing evolution of policies to eliminate SHS would be expected to protect women and their future children."

The Women’s Health Initiative program is funded by the National Heart, Lung, and Blood Institute. The authors have disclosed no relevant financial relationships.

Tobacco Control. Published online February 26, 2014. Abstract

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