Women currently comprise approximately half of the United States workforce. Many women are employed in occupations that require the use of respiratory protective equipment, such as N95 respirators. Some of these occupations include healthcare, laboratory workers, researchers, agriculture workers, and painters. Women may also wear respiratory protective equipment during outbreaks of infectious diseases, such as SARS and pandemic influenza, or for those who have allergies during times of high pollen counts. As researchers at the NIOSH, National Personal Protective Technology Laboratory, we received a number of inquiries regarding the safe use of respirators during pregnancy. Through this feedback we noted a knowledge gap regarding the safe use of respirators during pregnancy. We therefore undertook a study to look at oxygen levels and carbon dioxide levels in pregnant women wearing N95 respirators to determine if there were any harmful effects. For this study we recruited 22 healthy, non-smoking pregnant women who were in their second and third trimesters of pregnancy, and we compared them to 22 other women who were non-pregnant, but were matched with them for height, weight, and age. We tested them over one hour doing simple activities, such as standing, sitting, and pedaling a bicycle. During that time we measured their blood pressure, their heart rate, their breathing rate, their oxygen, and their carbon dioxide, and also the heart rate of the fetus. We also recorded their perceptions regarding any breathing difficulties that they may have had while wearing the respirator. In all of the categories that we measured, we noted no statistically significant differences to the effects of wearing a respirator between the pregnant and the non-pregnant women. We observed that the effects of wearing a respirator were generally quite mild; for example, the heart rate went up only two beats per minute, and the breathing rate decreased by only one breath per minute when wearing the N95. Respirators have electrical charges built in to their filters that improve the filter’s ability to capture particles. This also allows the N95 to be thinner and more breathable. In addition there are some N95 respirators that have an exhalation valve, which allows exhalation to be easier. There are quite a few reasons why individuals may find it harder to breathe when wearing an N95. For some individuals wearing an N95 respirator induces sensations of anxiety or claustrophobia; whereas for some other individuals wearing an N95 changes their normal nasal breathing pattern to mouth breathing, and that may be uncomfortable for them. For some individuals who have chronic medical conditions such as, poorly controlled asthma or chronic bronchitis, the additional breathing resistance of an N95 respirator may make it more difficult for them to breathe. We should note that in our study we only measured subjects over the course of one hour period of time, and so additional research is necessary in order to determine if wearing a respirator for longer periods of time has any ill-effects. Although all workers who are required to wear respiratory protective equipment for their occupational duties, must first undergo a medical evaluation. Any such pregnant worker with concerns, should contact her respiratory protection program manager regarding her concerns, and she may also wish to contact her obstetrician or any other licensed medical provider with expertise in respiratory protection, any of whom may request further evaluation.