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    Winter danger: carbon monoxide poisoning during pregnancy


    Dr Friedman is Resident Physician, Department of Obstetrics and Gynecology, Bridgeport Hospital, Bridgeport, Connecticut.

    Dr Stiller is Chief, Section of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Bridgeport Hospital, Bridgeport, Connecticut, and Clinical Professor of Obstetrics and Gynecology, Yale School of Medicine, New Haven, Connecticut.

    Neither of the authors has a conflict of interest to report in respect to the content of this article.

    Carbon monoxide (CO) is a colorless and odorless gas that is a byproduct of combustion and has the potential to quickly reach hazardous concentrations in poorly ventilated areas. In fact, accidental household CO poisoning is the most frequent cause of poisoning in pregnancy.1 Some of the more common sources of CO production include running vehicles, poorly maintained heating equipment, clogged chimneys, and poorly ventilated gas appliances. In cold winter months, it is important to remain vigilant for CO poisoning, as the presenting signs are often nonspecific.

    The maternal symptoms of acute CO poisoning range from relatively mild and nonspecific (eg, headaches, nausea, and vomiting) to more severe (eg, altered mental status or coma) as maternal levels of carboxyhemoglobin (COHb) increase. In nonsmoking women, the normal level of COHb ranges from 1% to 3%, but it can reach as high as 9% in those who smoke. In acute poisoning, levels may reach 30%–50%.

    The effects of CO poisoning on the developing fetus depend greatly on the gestational age of exposure and the dose. As a general rule, fetal injury is more likely when acute maternal CO poisoning is associated with more severe symptoms such as loss of consciousness. An anoxic event during the early gestational ages of embryogenesis or shortly after may be associated with anatomical malformations such as limb abnormalities or microcephaly, specifically in fetuses that survive to viability.2 At later gestational ages, severe exposures can be associated with the fetal neurological sequelae of anoxia, including but not limited to hypoxic ischemic encephalopathy, hypotonia, and cerebral palsy. Mortality rates for fetuses may be as high as 67% in severe intoxications. Generally, mild maternal exposures presenting with only headaches and nausea are more likely to result in favorable fetal outcomes.3


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    Perry Friedman, MD
    Dr Friedman is Resident Physician, Department of Obstetrics and Gynecology, Bridgeport Hospital, Bridgeport, Connecticut.


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