Yes, smelling gas can be harmful to an unborn child. Inhaling gas fumes during pregnancy can potentially lead to a number of health issues for the fetus, such as low birth weight and premature delivery. Studies have even linked prolonged exposure to higher levels of carbon monoxide in the home with an increased risk for neural tube defects in newborns, so it's important that pregnant women avoid any unnecessary contact with gas fumes or other volatile organic compounds (VOCs). Taking extra precautions around natural gas appliances like stoves and water heaters is especially important because these are known sources of VOCs. Additionally, having your home tested for high levels of indoor air pollution before and after you become pregnant can help protect both mother and baby from potential harm due to chemical exposure.