Passive smoking is called secondhand smoke, pregnant women occasionally smell secondhand smoke will not have any harm, long-term smell secondhand smoke may increase the chances of fetal miscarriage and fetal arrest, developmental deformities, and cause other diseases. 1. No harm: pregnant women only occasionally sniff second-hand smoke, sniffing second-hand smoke time is relatively short, there will be no harm in this case. 2. Miscarriage and Fetal Arrest: Passive smoking for more than 15 minutes is considered to be established when the phenomenon of secondhand smoke, tobacco through the combustion of a large number of toxic and harmful gases, such as coal tar, nicotine, carbon monoxide, etc., as a result of nicotine and its metabolites in the role of the tobacco, caused by the body of the value of the progesterone is low, may occur spontaneous abortion or fetal arrest. 2. Developmental deformities: some harmful substances in secondhand smoke may lead to cell mutation, damage to germ cells may change the genetic factors, resulting in fetal developmental deformities or mental retardation. 4. triggering other diseases: second-hand smoke contains nitric oxide, heavy metals, radioactive dust and particulate matter, particulate matter sucked into the lungs will produce damage to the respiratory mucosa, may cause laryngitis, bronchitis and other diseases, children are prone to asthma, pneumonia, bronchitis and other diseases after birth. Therefore, it is recommended to stay away from second-hand smoke during pregnancy and try to live in a smoke-free environment.