Long-term breathing of severely polluted air or blindly wearing a mask may affect the healthy development of the fetus. Therefore, it is recommended that pregnant women do not wear masks when the air quality index is below 150; if it exceeds 300, they should try to avoid going out; Choose a mask with a relatively large cup body with exhalation valve on the front (non-foldable) and protection level not higher than N95 (or equivalent). If it is not necessary (for example, it is not sensitive to odors in exhaust gas or second-hand smoke), you do not need to choose the type with activated carbon layer in this type of mask.