Pregnant women are generally fine with occasional sniffing of automobile exhaust, but prolonged sniffing of large quantities of automobile exhaust will have a certain effect. Automobile exhaust contains carbon monoxide, hydrocarbons, lead and other harmful substances, and the occasional sniffing will not affect the pregnant woman and the fetus. However, if you sniff car exhaust for a long time, it may directly pass through the placenta into the fetus, and the harmful substances will also affect the fetus, and even the pregnant woman may experience dizziness, nausea and other adverse reactions. Therefore, to be on the safe side, it is not recommended for pregnant women to smell car exhaust fumes frequently during pregnancy. During pregnancy, in addition to avoiding exposure to harmful substances, pregnant women also need to pay more attention to regular maternity checkups, and promptly consult a doctor after experiencing symptoms of physical discomfort.