Carbon dioxide. Carbon dioxide (chemical formula CO2) is a colorless gas with a density about 60% higher than that of air (1.225 g/L) that is odorless at normally encountered concentrations. Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms.
You should only do ballet in pregnancy if you are used to it. Ballet stretches can place a lot of pressure on your joints, especially your pelvic joints, and standing on one leg can cause pain in your pelvis.
Most doctors do not mind pregnant women flying during their first trimester; it is actually during the third trimester that pregnant women are told not to fly as it could trigger labor. Flying during the first trimester may be unadvisable if it involves too much stress which could harm the baby and the mother. It is also unadvisable if the woman has had a history of miscarriages or ill health. Flying may cause air sickness which pregnant women are particularly vulnerable to.